Download Review: Gas-phase ion chemistry of the noble

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F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)
Received: 27 October 2011 n Accepted: 2 November 2011 n Publication: 24 November 2011
EUROPEAN
JOURNAL
OF
MASS
SPECTROMETRY
openaccess
Review
Gas-phase ion chemistry of the noble gases:
recent advances and future perspectives
Felice Grandinetti
Dipartimento per la Innovazione nei Sistemi Biologici, Agroalimentari e Forestali (DIBAF), Università della Tuscia, L.go dell’Università, s.n.c.,
01100 Viterbo, Italy. E-mail: [email protected]
This review article surveys recent experimental and theoretical advances in the gas-phase ion chemistry of the noble gases. Covered
issues include the interaction of the noble gases with metal and non-metal cations, the conceivable existence of covalent noble-gas
anions, the occurrence of ion–molecule reactions involving singly-charged xenon cations and the occurrence of bond-forming reactions involving doubly-charged cations. Research themes are also highlighted, which are expected to attract further interest in the
near ­future.
Keywords: gas-phase ion chemistry, mass spectrometry, noble gases, theoretical calculations
Acronyms
CAD = collisionally-activated dissociation
CI = chemical ionization
CID = collision-induced dissociation
DET = dissociative electron transfer
DFT = density functional theory
EI = electron ionization
ET = electron transfer
FT-ICR = Fourier-transform ion cyclotron resonance
IE = ionization energy
IRPD = infrared photodissociation
IT-MS = ion trap mass spectrometry
KER = kinetic energy release
MIKE = mass-analyzed ion kinetic energy
PA = proton affinity
PT = proton transfer
SIFT = selected-ion flow tube
ToF = time of flight
TQ = triple quadrupole
Introduction
The chemistry of the noble gases is currently the focus of
intense experimental and theoretical interest.1,2 At the beginning of the millennium, breakthrough advances such as the
synthesis of HArF,3 a chemically-bound argon compound
observable in low-temperature solid matrices and various
achievements in xenon chemistry,4–8 heralded a renaissance
in this field.9 Unceasing progress was actually made in the
last decade, not only in the preparation of xenon and krypton
ISSN: 1469-0667 doi: 10.1255/ejms.1151
compounds,10–14 but also in the study of noble gas ­chemistry
under less conventional environments, such as the cold
matrices2,15–18 or the vacuum.19 The isolated conditions of
the gas phase are, in particular, ideally suited to explore the
structure, stability and reactivity of noble gas ionic species.
As a matter of fact, first hints to this chemistry were reported
well before the Bartlett’s synthesis that dates the official
beginning of noble gas chemistry.20–22 Thus, in 1925, Hogness
© IM Publications LLP 2011
All rights reserved
424
and Lunn23 studied the ionization of H2 in the presence of
He and noted the formation of HeH+. An ion with m/z = 6 was
also observed and assigned as HeH2+. Meanwhile, Lind and
Bardwell24,25 recognized the ability of noble gas ions to c­ atalyze
the ­polymerization of acetylene, cyanogens and hydrogen
cyanide. They suggested the active role of clustering about
the ionic centers and, 35 years later, a Xe(CN)2+ complex was
actually observed by mass spectrometric methods.26 In 1933,
Pauling predicted27 the “normal states” of He2+ and He22+ and
the singly-charged He2+, Ne2+ and Ar2+ were soon observed by
Tüxen28 in the mass spectra of ionized helium, neon and argon
(He22+ was also detected in 198529 by charge stripping of He2+).
Kr2+ and Xe2+ were observed by Hornbeck and Molnar in 195130
and the heteronuclear diatomic ions of all the rare gases
(except radon) were reported in 1963.31 In addition, in the early
1960s, several investigators had already observed the formation by ion–molecule reactions of various cationic species
with noble gases bound to carbon, nitrogen, oxygen and halogens.32–36 Xenon–alkyl and krypton–alkyl cations were also
produced from the b–-decay of the corresponding isoelectronic
radioactive alkyl halides.37–39 Over the years, the number of
observed gaseous noble gas ions has considerably increased
and the family currently includes diatomic and small-size
polyatomic species as well as large-size ionic clusters and
encapsulated products. Theoretical calculations have also
been extensively used to aid the interpretation of the experiments and to investigate the conceivable existence of still
uncovered molecular species. The matter is, indeed, continuously growing and developing and the present review covers,
in particular, exemplary advances achieved in the last decade.
Noble gases as ligands of ionic
species
Review of Gas-Phase Chemistry of Noble Gases
­experimentally43–47 and theoretically,48–53 and also in connection with the use of superfluid helium as a gentle matrix for
the study of molecular structure and reactivity.54,55 Within this
description, the simplest metal ion–noble gas complexes are
the diatomic singly-charged M+∙Ng. The values of the IE (the
acronyms used throughout the text are listed in the List of
acronyms at the begining of this paper) of the noble gases,
listed in Table 1, are invariably higher than the IE of any metal
atom M,56 so any ground-state M+∙Ng, therefore, consists of
a M+ ion which interacts with a Ng atom. Within this description, it is of interest to appreciate whether the M+–Ng bond
is a purely electrostatic and dispersion interaction (“physical”
bonding) or whether there is an extra component due to Lewis
acid–base covalent interaction (“chemical” bonding). The
extensive experimental and t­heoretical information available
up to 2001 on the bond distances, dissociation energies and
spectroscopic properties of the diatomic M +∙Ng (M+ = maingroup or transition metal cation; Ng = He–Xe) was reviewed
nearly ten years ago.57 It was shown, in particular, that when
all the physical terms out to 1/R8 were properly included in
a “long-range-forces” model potential, almost all the data
available for the potential energy curves of the diatomic M+∙Ng
could be adequately explained without having to invoke extra
covalent forces. Accurate calculations performed in the last
decade on various metal ions–noble gas complexes58–70 led
to further insights into the M+–Ng interaction. In particular,
the data obtained for the systems comprising the alkali–58–62
and the alkaline–earth metal cations64–66 are listed in Tables 2
and 3. For the alkali–cation–Ng complexes, the model potential analysis confirmed63 that all these systems can actually
be described in physical terms. It was pointed out, however,
Table 1. Ionization energies (IE)a and polarizabilities (a)b of the
noble gases.
Complexes with metal ions: from diatomic to
cluster-size systems
The closed-shell, monoatomic noble gases are, in principle, the
simplest ligands to attempt the preparation of co-­ordination
compounds. It was, however, only in 20004 that the isolation of a
solid salt of the square–planar cation, AuXe42+ (with two Sb2F11–
counterions) definitively demonstrated the ability of xenon
to behave as a classical ligand toward metal cations. Other
Au–Xe and Hg–Xe cations were subsequently reported, 40–42
but the synthesis of metal complexes containing noble gases
other than xenon still remains a fascinating ­challenge. On the
other hand, under the isolated conditions of the gas phase,
all the “inert” elements, including the lightest helium and
neon, have a distinct tendency to form complexes with metal
ions, mainly cations but also anions. The observed species
range from diatomic to cluster-size systems, which contain
up to several tens of Ng atoms. Remarkable examples in this
regard are the “snowball” complexes ensuing from the ionization of helium nanodroplets doped with metal atoms. These
systems are currently being intensively investigated, both
2
Ng
IE
(eV)
He
24.587
Ne
21.564 d
P1/2–2P3/2
(eV)c
a
(Å3)
0.205
0.097
0.396
0.177
1.641
0.666
2.484
1.306
4.044
3.831
5.3
e
21.661
Ar
15.759d
15.936
Kr
e
14.000d
14.666
Xe
e
12.130d
13.436
Rn
e
10.748d
e
14.579
a
Taken from Reference 72
b
Taken from Reference 56
c
Energy difference between the 2P1/2 and 2P 3/2 electronic states of Ng+
d
With formation of 2P 3/2
e
With formation of 2P1/2
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)425
Table 2. Theoretical bond distances (Re), dissociation energies (De), and harmonic vibrational frequencies (we) of the complexes of the noble
gases with the alkali metal cations (taken from References 58–62).
M+
Ng
Re
(Å)
De
(kJ mol–1)a
we
(cm–1)
Li+
He
1.896
 7.8
272
Na+
K+
Rb+
Cs+
Fr+
a
Ne
2.038
12.0
229
Ar
2.364
28.3
270
Kr
2.520
34.2
262
Xe
2.716
42.7
265
Rn
2.806
47.4
261
He
2.324
 3.9
155
Ne
2.472
 6.1
107
Ar
2.780
16.0
125
Kr
2.920
20.3
118
Xe
3.104
26.1
119
Rn
3.192
29.5
116
He
2.825
 2.2
100
Ne
2.921
 3.9
 72
Ar
3.215
10.3
 82
Kr
3.356
12.9
 74
Xe
3.558
16.5
 73
Rn
3.641
18.8
 71
He
3.070
 1.7
 82
Ne
3.140
 3.2
 57
Ar
3.425
 8.6
 63
Kr
3.560
10.9
 53
Xe
3.750
14.2
 51
Rn
3.835
16.1
 48
He
3.360
 1.3
 67
Ne
3.400
 2.6
 47
Ar
3.640
 7.4
 53
Kr
3.760
 9.6
 44
Xe
3.950
12.5
 42
Rn
4.030
14.2
 38
He
3.470
 1.2
 62
Ne
3.490
 2.4
 44
Ar
3.710
 7.1
 49
Kr
3.830
 9.3
 40
Xe
4.010
12.2
 36
Rn
4.090
13.9
 32
Depth of the potential well with no ZPE
that the employed long-range-force potential cannot account
quantitatively for all the effects, particularly at the small
bond distances. This probably reflects minor breakdowns
of the model at the small internuclear separations, where
the “lengths” of the induced multipoles become significant
compared to the equilibrium bond distance. In any case, these
small quantitative inadequacies do not limit the validity of the
model in describing the periodic trends of the structure and
stability of the diatomic M+∙Ng. In this regard, it is of interest
to note the unusual trends of the bond lengths (Re) and the
426
Review of Gas-Phase Chemistry of Noble Gases
Table 3. Theoretical bond distances (Re), dissociation energies (De), and harmonic vibrational frequencies (ωe) of the complexes of the noble
gases with the alkaline–earth metal cations (taken from References 64-66).
M+
Ng
Re
(Å)
De
(kJ mol–1)a
we
(cm–1)
Be +
He
2.924
  1.6
 76
Ne
2.454
  4.9
 65
Ar
2.084
  53.0
364
Kr
2.221
 72.4
366
Xe
2.407
 98.6
373
Mg+
Ca
+
Sr+
Ba
+
Ra+
a
Rn
2.486
113.5
371
He
3.482
  0.9
 46
Ne
3.145
  2.4
 43
Ar
2.822
 15.5
105
Kr
2.884
 23.7
118
Xe
3.018
  35.6
135
Rn
3.064
 43.5
141
He
4.259
  0.4
 26
Ne
3.760
  1.3
 25
Ar
3.256
  8.9
 61
Kr
3.305
 14.4
 70
Xe
3.457
 21.3
 78
Rn
3.487
  26.2
  82
He
4.547
  0.3
 21
Ne
4.005
  1.1
 20
Ar
3.385
  7.7
 47
Kr
3.433
 12.6
 51
Xe
3.591
  18.7
 55
Rn
3.617
 23.2
 55
He
4.950
  0.3
 17
Ne
4.291
  0.9
 15
Ar
3.385
  8.3
 59
Kr
3.479
 13.1
 54
Xe
3.653
 18.8
 52
Rn
3.709
  22.9
  50
He
4.885
  0.3
 18
Ne
4.276
  0.9
 16
Ar
3.759
  5.8
 34
Kr
3.775
  9.5
 35
Xe
3.917
 14.0
 36
Rn
3.944
 17.6
 35
Depth of the potential well with no ZPE
­dissociation energies (De) of the noble gas complexes of the
alkaline–earth cations.64–66 As shown in Table 3, for any M+∙Ng
(M+ = Be+–Ra+), the M+∙He complex has a large Re and a low De,
the M+∙Ne complex has a smaller Re and a slightly higher De
and there is a sudden major decrease in Re for M+∙Ar, accompanied by a huge (5–10-fold) increase in De. The values of Re
and De then both increase, but more slightly, passing from
M+∙Kr to M+∙Rn. For comparison, in the alkali–ion complexes
(see Table 2), irrespective of the metal cation, the values
of both Re and De follow a regular increasing trend passing
from M+∙He to M+∙Rn (M+ = Li+–Fr+). The unusual trends in the
properties of the group 2 complexes, in particular the marked
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)427
drop in Re and the concomitant marked rise in De passing from
M+∙Ne to M+∙Ar, were explained by noting64–66 that the s–p or
s–d mixing of the singly-occupied ns orbital of M+, induced by
the Ng atom, causes the electron density on M+ to move offaxis, away from the incoming Ng. This reduces the electron
repulsion and allows a closer M+–Ng approach, resulting in
an increase in the attractive terms, especially the dispersion
interactions. This M+/Ng synergistic effect becomes particularly important in the passage from Ne to Ar but is, instead,
essentially negligible for the least polarisable He. As a matter
of fact, in the M+∙He complexes, the distortion of the electronic
cloud of the helium atom is, in general, negligible and the M+–
He interaction is truly electrostatic. Based on this observation,
it was possible to derive71 a consistent set of ionic radii of M+,
RHe, obtained as the Re value of the M+∙He complex minus the
van der Waals radius of He (estimated as one-half of the Re
value of He2, or 1.49 Å72). This definition was also extended
to the M2+ cations and to the M– anions,71 and the obtained
RHe were compared with the ionic radii obtained from X-ray
crystallography, as well as with estimates from gas-phase
MF, MF+, MO and MOM molecules and ions. This suggested
interesting considerations about bonding in ionic crystals and
in gas-phase oxides and fluorides.71
Overall, the theoretical work performed in the last decade
confirms that the vast majority of the diatomic M+∙Ng are held
together by physical forces, even though chemical factors
such as the shape of the electron density of the cation and
its hybridization may be operative. There are, however, some
noticeable exceptions, such as the bonds of Au+ with argon,
krypton and xenon, that possess a pronounced contribution
of covalent character. Thus, in 1995, Pyykkö predicted73 the
existence of Au+∙Ng (Ng = Ar, Kr, Xe) by relativistic calculations
and suggested that most of the bonding interaction was covalent in character and strengthened along the Ar–Kr–Xe series.
The Au+∙Xe complex was subsequently observed in the gas
phase,74 and its De was estimated as 125.9 kJ mol–1. However,
in the meantime, Read and Buckingham75 had questioned the
conclusion by Pyykkö73 and suggested that the Au+–Xe interaction could be adequately described in terms of the longrange effects of polarization and dispersion. Recent accurate
calculations76–78 solved the question in favor of the covalent
proposal. The theoretical parameters of the interaction potentials of the noble gases with the coinage metal cations Cu+,
Ag+ and Au+,76 listed in Table 4, were slightly refined for the
gold complexes77 and the obtained values were employed for
a model potential analysis.77 The obtained results pointed out
a clear covalent component in the bonding of Au+ to Kr and
Xe, with some evidence for such bonding between Au+ and Ar.
No evidence was obtained for a covalent contribution to the
bonding between Au+ and Ne instead. The same conclusion
was, indeed, anticipated by accurate fully relativistic calculations.78 For all three Au+∙Ng complexes (Ng = Ar, Kr, Xe), it was
Table 4. Theoretical bond distances (Re), dissociation energies (De), and harmonic vibrational frequencies (ωe) of the complexes of the noble
gases with the coinage metal cations Cu+, Ag+ and Au+ (taken from Reference 76).
M+
Cu+
Ag+
Au+
a
Depth of the potential well with no ZPE
Ng
Re
(Å)
De
(kJ mol–1)a
we
(cm–1)
He
1.95
  9.4
216
Ne
2.34
 10.1
120
Ar
2.30
  50.4
200
Kr
2.37
 70.5
183
Xe
2.49
 99.3
182
Rn
2.56
110.8
183
He
2.41
  4.7
127
Ne
2.66
  6.9
 89
Ar
2.64
 31.2
138
Kr
2.68
 46.4
126
Xe
2.76
  70.2
128
Rn
2.82
 81.6
200
He
2.44
  4.6
122
Ne
2.73
  6.8
 83
Ar
2.53
 44.8
160
Kr
2.55
 73.6
148
Xe
2.61
120.4
151
Rn
2.67
140.6
135
428
found that the Au–Ng bond is characterized by a pronounced
charge accumulation in the middle of the Au–Ng internuclear region, which is typical of a covalent bond. Not unexpectedly, its extent was found to increase as one moves from
Ar to Xe. It is also of interest to note that recent DFT calculations on the Au+(Ar)n clusters with n up to 6,79 also revealed a
large amount of charge transfer between gold ions and argon
atoms. The largest Au+(Ar)4, Au+(Ar)5 and Au+(Ar)6 were, in
particular, predicted to be, respectively, a distorted tetrahedron, a trygonal bipyramid and a regular octahedron.
Passing from the diatomic M+∙Ng to the polyatomic M+(Ng)n
(n ≥ 2), the character of the M+–Ng interaction is not expected
to change and the most interesting questions concern the size
of the achievable systems and their structure and stability. In
the last two decades, considerable progress has been made in
the experimental and theoretical investigation of the
complexes of various singly-charged main-group and
transition-­m etal cations with neon, argon, krypton and
xenon.79–94 The current interest is, however, mainly focused on
the somewhat special group of the M +(He) n cluster-size
systems obtained from the ionization of metal-doped helium
nanodroplets.43–53 In typical experimental set-ups,44,46 He
droplets are first produced by the supersonic expansion of
pre-cooled helium gas at stagnation pressures of 20–60 bars
through a nozzle of 5–10 μm diameter at temperatures of
8–14 K. In these conditions, the mean droplet size is in the
range of 103–107 atoms. The beam enters a pick-up chamber
containing a heated oven, where a vaporized metal, M, aggregates to clusters inside the He droplets. For the alkali metals,
the clusters are attached on the surface of the droplet
instead.95 The metal-cluster doped droplets are subsequently
ionized by a laser radiation or by EI and the ensuing ionic
species are detected by a quadrupole or a ToF mass spectrometer. Singly-charged M+(He)n are typically observed which
contain up to hundreds of helium atoms and the size distributions derived from the mass spectra furnish, in particular,
information on the existence of “magic” numbers, typically
associated with the closure of shell structures around the
central cation. Before discussing relevant experimental
results, it is of interest to examine the description of these
systems offered by the theoretical calculations.48–53 In general,
it is accepted that, in liquid helium, a positive ion, M+, is localized at the center of the droplet and forms a “snowball”, with
well-defined shells of He atoms, which possess a solid-like
order, at least in the first surrounding shell. However, at
variance with the clusters of the heaviest noble gases, due to
quantum effects arising from the low mass of He, the groundstate averaged structures of the M +(He)n can qualitatively
deviate from the “static” picture offered, for example, by the
“hard-sphere” packing model85 or by the equilibrium structures computed by ab initio or DFT calculations. The M+(He)n
have, therefore, been investigated by Monte Carlo methods,
with special attention to systems containing the alkali and
alkaline-hearth singly-charged cations.48–50,53 In particular, a
path integral Monte Carlo study has very recently been
reported53 on 4He droplets doped with Na+, K+, Cs+, Be+ and
Review of Gas-Phase Chemistry of Noble Gases
Mg+ which contain between 14 and 128 4He atoms. For all
these systems, the snowball model proved to be adequate in
describing the distribution of the 4He atoms around M+. In
particular, at least in the first two solvation shells, the helium
density resulted in being well above the freezing density of
bulk 4He (0.0258 Å–3), so that some kind of solid order is invariably predicted. However, the number of surrounding helium
shells (two or three), the number of 4He atoms per shell and
the degree of localization of the helium atoms within the shells
proved to be sensitive to the nature of M+. The most solid-like
structure is Na+(He)n, which presents three rather rigid shells
of 4He atoms, characterized, respectively, by an icosahedral,
dodecahedral and icosahedral order. This reflects a rather
steep Na+–He potential and a rather strong Na+–He interaction. For the other investigated M+ ions, (M+ = K+, Cs+, Be+, Mg+),
the M+–He interactions are, in general, weaker than Na+–He
(see Tables 2 and 3) and, in fact, several effects were noticed
which, overall, indicate less rigidity of the M+(He)n with respect
to Na+(He)n and a more ambiguous definition of magic shells
of 4He atons around the cation. For example, while the number
of 4He atoms in the first shell of Na+(He)n is invariably predicted
to be 12 for n = 32, 64 and 128, the number of 4He atoms in the
first shell of the other complexes slightly depends on the size
of the droplet and ranges between 14 and 15 for K+(He)n and
Be+(He)n and between 17 and 18 for Cs+(He)n. At variance with
Na + (He) n, these numbers do not correspond to regular
polyedra. In addition, in the passage from Na+ to the other
investigated cations, there are pronounced “exchanges”
between the atoms which form the first two solvation shells.
These fluctuations are particularly evident for Mg+(He)n, for
which a previous study48 had indeed suggested a liquid-like
structure of the first shell around the cation. A similar conclusion was held for Ca+(He)n48 and it has also to be mentioned
that it was previously noted96 that, in liquid He, Mg+ does not
form a snowball but rather a “bubble”, namely a cavity
surrounded by compressed, less structured and, most likely,
not solidified helium. Monte Carlo calculations have also
recently been reported for Pb+(He)n.52 The first solvation shell
is completed for n = 17, but the second shell resulted in being
much less clearly distinguished from the first shell. As for the
experimental results, M+(He)n clusters have been observed for
Na+,46 K+,46 Rb+,46,47 Cs+,46 Mg+,44 Zn+,44 Cd+,44 Ag+ 44 and Pb+.43,44
For Na+ and K+, the observed snowball progression46 is limited
to less than 11 He atoms and it is therefore not possible to
make comparisons with the large-size structures investigated
by the calculations. 48,49,53 For Rb + and Cs +, the observed
clusters distribution 46 extends, instead, up to n = 41 and
characteristic steps in the mass spectra indicate, in particular,
the closure of the first shell around the cation at n = 14 for Rb+
and at n = 16 for Cs+. These values are, therefore, low-shifted
by one unit of mass with respect to the most recent theoretical
prediction.53 For Mg+, the observed complexes contain up to
150 He atoms.44 A shell closure is observed at n = 19–20, which
is up-shifted by one to two units of mass with respect to the
most recent theoretical prediction.53 For Pb+(He)n,43,44 the shell
closure observed at n = 17 is, instead, in perfect agreement
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)429
with the calculations.52 Interesting results were also obtained
from the study of Ag+(He)n.44 The observed progression extends
up to beyond n = 150 and the clear steps in the ionic distributions observed at n = 10, 12, 32 and 44 were assigned to two
different snowball structures. The first has 10 He atoms in the
first shell and 32 atoms in the second shell, while the second
structure has its first and second closing, respectively, at n = 12
and n = 44. It was suggested that these two structures arise
from Ag+ ions in different electronic states.44 It has, however, to
be noted that the observed values could simply reflect different coordination modes around Ag+, without invoking different
electronic states of the cation. It is interesting to note that
attachment of He atoms to Ag2+ and Ag3+ was also observed,44
but no evidence for shell closing was obtained. Ionic clusters
built around Na2+ and Cs2+ were also detected in the mass
spectra of Na- and Cs-doped helium nanodroplets. 46 The
abundance of these Na2+(He)n (n ≤ 3) and Cs2+(He)n (n ≤ 7) is,
however, one order of magnitude lower than the snowballs
formed around Na+ and Cs+. Previous calculations on M2+(He)n
(M = Li, Na, K)50 had shown that, for K2+, the solvent cage is
asymmetric and dominated by the He–He network formation.
For Li2+ and Na2+, a rigid snowball structure with a regular
configuration is formed within the first shell that encloses the
solvated cation (n = 6), followed by more delocalized collocations of the solvation atoms for clusters beyond this size. Such
additional ligands form symmetric solvent cages at the two
ends of each ionic dimer. Overall, considerable progress has
been made recently in the investigation of the qualitative and
also quantitative aspects of the M+(He)n clusters observed in
helium nanodroplets. Further work is, however, still needed to
fully understand the structural and dynamic properties of
these fascinating objects.
Pa s s i n g f ro m M + t o M 2 + , t h e s t a b i l i t y o f a n y
(formal) M2+(Ng)n (n ≥ 1) with respect to the loss of Ng atom(s)
generally increases. This essentially reflects the dependence
of the attractive polarization term of the M2+–Ng interaction
potential on the square of the ionic charge. This effect is
clearly appreciated, for example, by comparing the predicted
stabilities of the group 2 complexes M2+∙Ng (M2+ = Be2+–Ra2+;
Ng = He–Rn),64–66 listed in Table 5, with the data of the corresponding M+∙Ng64–66 (see Table 3). The actual observation of
the doubly-charged M2+(Ng)n complexes is, however, much
more difficult than the corresponding singly-charged species.
The experimental work must, in fact, contend with two facts.
First, the cross sections of double ionization processes are, in
general, lower than those of single ionizations. In addition, the
stability of any diatomic M2+∙Ng and, in general, of any doublycharged M2+(Ng)n, strongly depends, especially for Ng = Ar, Kr
and Xe, on the favorable influence of kinetic factors. Thus,
while the first IE of any metal atom, M, is invariably lower than
the IEs of the noble gases, the second IE of M56 is, in general,
still lower than the IE of He and Ne, but higher than the IE of
Ar, Kr and Xe. Therefore, when the electron transfer from Ng to
M2+ is exothermic, any formed M2+∙Ng can actually be detected
in the gas phase only if it is protected by a sufficiently high activation barrier from the spontaneous dissociation into M+ and
Ng+. This metastability is the result of an “avoided crossing”
between an electronic state converging at large interspecies
separations to dication plus neutral (M2+ + Ng) and a purely
repulsive electronic state correlating with the charge-separated asymptote (M+ + Ng+).97,98 The M2+(He)n are invariably
stable with respect to the loss of He atom(s) and various M2+∙He
(M2+ = V2+, Fe2+, Ta2+, Mo2+, Rh2+, Pt2+, Ir2+) and M2+(He)2 (M2+ = Pt,
W) have so far been detected by field-ion microscopy.99 Other
helide and dihelide dications have also recently been predicted
by theoretical calculations.100–102 It is of interest that largesize M2+(He)n with n up to tens have recently been observed
from the ionization of helium nanodroplets doped with Mg,
Ag and Pb.43,44 For Ag2+(He)n and Mg2+(He)n, the observed
magic numbers were 4 and 6 and 4 and 8, respectively,44 while
the closure of a first solvation shell at n = 12 was inferred
for Pb2+(He)n. The latter result is of particular interest, as it
stresses the importance of including quantum effects to properly describe the relative stability of the cationic-doped helium
snowballs. A theoretical search for conceivable Pb 2+(He)n
global minima based on electronic-structure methods51 had,
in fact, suggested the special stability of Pb2+(He)15 and the
conceivable existence of coordination numbers higher than
those predicted for regular icosahedral structures. However,
in keeping with the experiments,43,44 subsequent Monte Carlo
calculations52 revealed that, for Pb2+(He)n, the first solvation
shell is closed at n = 12 and it gradually softens by additional
helium atoms, which start to form a distinct second shell
only at n = 16. The Pb2+(He)15 is a special size only in the sense
that, as with Pb2+(He)12, it is the last member of a structural
or energetic motive. The argon complexes Mg2+(Ar)n were
also so far observed,80 and maxima of intensity at n = 4 and 6
were noticed in the mass spectra. Subsequent calculations81
disclosed regular tetrahedral and octahedral coordinations.
The second IE of Mg, 15.03 eV,56 is indeed lower than the IE
of Ar and any Mg2+(Ar)n is therefore predicted to be thermochemically stable with respect to the loss of Ng atoms. On the
other hand, the more recently observed103 Cu2+∙Ar, Ag2+∙Ar and
Au2+∙Ar are noticeable examples of metastable species. The
values of the second IE of Cu (20.29 eV),56 Ag (21.49 eV)56 and
Au (20.5 eV)103 are, in fact, definitely higher than Ar and, as
disclosed by the calculations,103 their observation is actually
allowed by barriers large enough to prevent their fast decomposition. The second remarkable result from this study 103
was the high relative intensities of the M2+(Ar)4 and M2+(Ar)6
cations (M2+ = Cu2+, Ag2+, Au2+), theoretically shown to consist of
square–planar structures of D4h symmetry, with the additional
two atoms in Jahn–Teller distorted axial sites. It is of interest
that the M2+(Ar)4 are the lightest congeners of the synthesized
gold–xenon cation AuXe42+.4 This is indeed a first example
of the opportunities offered by gas-phase ion chemistry to
observe noble-gas ionic species that are elusive or even unattainable in the condensed phases.
The above-mentioned Mg2+(Ar)n80 and M2+(Ar)n (M2+ = Cu2+,
Ag2+, Au2+)103 were produced into cluster ion sources by laseror thermal vaporization of pure metal targets. On the other
hand, the recently observed Ba2+∙Ng (Ng = Ar, Kr, Xe)104 were
430
Review of Gas-Phase Chemistry of Noble Gases
Table 5. Theoretical bond distances (Re), dissociation energies (De), and harmonic vibrational frequencies (ωe) of the complexes of the noble
gases with the alkaline-hearth metal dications (taken from References 64–66).
M2+
Ng
Re
(Å)
De
(kJ mol–1)a
we
(cm–1)
Be2+
He
1.428
 90.6
902
Ne
1.577
131.4
675
Ar
1.867
297.6
692
Kr
2.009
357.4
635
Xe
2.197
442.3
594
Mg2+
Ca2+
Sr2+
Ba2+
Ra2+
a
Rn
2.288
484.4
564
He
1.885
  32.9
462
Ne
2.035
 50.5
307
Ar
2.318
130.3
328
Kr
2.453
163.5
297
Xe
2.632
213.5
284
Rn
2.711
240.6
271
He
2.351
 14.8
279
Ne
2.461
 24.9
183
Ar
2.735
  67.8
200
Kr
2.865
 87.6
179
Xe
3.040
114.2
173
Rn
3.115
128.8
165
He
2.565
  10.9
224
Ne
2.654
 19.1
141
Ar
2.903
 54.8
151
Kr
3.026
 71.8
128
Xe
3.203
  95.3
120
Rn
3.265
107.5
111
He
2.842
  7.6
176
Ne
2.907
 13.9
111
Ar
3.130
  42.1
122
Kr
3.244
 56.0
101
Xe
3.413
 75.5
 94
Rn
3.481
  86.4
  85
He
2.947
  6.7
160
Ne
3.001
 12.4
101
Ar
3.214
 38.5
111
Kr
3.326
 51.7
 89
Xe
3.495
 69.9
 81
Rn
3.562
 80.0
 72
Depth of the potential well with no ZPE
obtained by the direct addition of Ba2+ (generated by electrospray ionization from BaCl2 solutions) to Ng atoms in helium
bufffer according to Reaction (1)
Ba2+ + Ng + He ® Ba2+∙Ng + He
(1)
The dicoordinated Ba(Xe)22+ was also observed and a weak
noticed signal was also tentatively assigned as Ba2+∙He. No
Ba2+∙Ne was detected instead. The remarkable occurrence of
Reaction (1) likely reflects a second IE of Ba, 10.00 eV,56 that is
definitely lower than the IE of any Ng. It was also observed104
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)431
that the rate of formation of the Ba2+∙Ng and the strength of
the interaction between Ba2+ and Ng increase by increasing
the polarizability of the noble gas atom. This trend is consistent with the theoretically predicted stabilities of the Ba2+∙Ng
complexes66 (see Table 5).
The formation of noble gas complexes with metal cations
in high oxidation states (Mz+; z ≥ 3) is typically prevented both
by the difficulties of producing appreciable intensities of Mz+
and by the occurrence of largely exothermic charge-transfers
between Mz+ and Ng. Thus, only a few helium episodes such
as W(He)n3+ (n = 2–4) were so far observed. 99 The structure
and stability of the multiply-charged M z+(Ng)n is, however,
of theoretical interest. Thus, stimulated by the synthesis
of AuXe 4 2+ (Sb 2 F 11 – ) 2 , 4 the tetra (square–planar) and
­exa-coordinated (octahedral) complexes of Ar, Kr and Xe with
the multiply-charged cations Ni2+, Zn2+, Pt2+, Au2+, Hg2+, Cr3+,
Co3+, Rh3+, Ir3+, Au3+, Pt4+, Mo6+ and W6+ were examined.105
For any Ng, the stability of the Mz+(Ng)n complexes (n = 4, 6),
measured as the energy required for the loss of the four or six
Ng atoms, increases by increasing the oxidation state of the
metal and, for any metal, increases in the order Ar < Kr < Xe.
The complexation energies per Ng atom typically range from
nearly 65–150 kJ mol–1 to 550–750 kJ mol–1 and may arrive up
to 1500–1675 kJ mol–1 for MoXe66+ and WXe66+. The conclusion
was reached105 that various trivalent, tetravalent and hexavalent transition-metal complexes of xenon and krypton may be
intrinsically stable.
The high stabilities of the M z+Ngn complexes (z ≥ 2) with
respect to the loss of Ng atoms could suggest a prevailing
covalent contribution to the Mz+–Ng interaction. However,
theoretical calculations106 performed to explore the nature
of the Au–Ng bond in the Au2+(Ng)4 complexes (Ng = Ar, Kr, Xe)
revealed that, even for xenon, the gold-noble gas bonding is
still dominated by electrostatic interactions. The Au–Xe bond
was, however, noticed to be somewhat different from the Au–
Ar and Au–Kr bonds, as a higher electron transfer from gold to
the Ng atoms is observed in the xenon complex.
It is of interest to close this survey of noble-gas complexes
with metal cations by mentioning two very recent studies107,108
performed by IRPD spectroscopy on the mixed H 2 O/Ar
complexes of Mn+, Mn2+, Sc+ and Sc2+. They are, in fact, good
examples of the application of the so-called “noble gastagging” technique, that is currently extensively used to
investigate the spectroscopic properties of a variety of ionic
species.109,110 Briefly, in this methodology, one or more Ng
atoms are attached to ions which contain, for example, O–H
or N–H groups. The stretching frequencies of these groups
are then excited by IR photons and, when the excitation is on
resonance, absorption occurs and the energy flows from the
O–H or N–H stretch into other complex vibrations via intramolecular vibrational relaxation. A fraction of the excited ions
then fragment by losing the Ng atom(s) and the fragment
ion intensity is recorded as a function of the IR frequency.
Resolved, or partially-resolved, rotational structures are also
sometimes observed. Therefore, in the noble gas-tagging
technique, the Ng atoms behave as “messengers”, that signal
the photon absorption by the core ion. In the ideal situation
of totally unperturbing Ng atoms, the observed IR spectrum
is virtually identical to that (otherwise unachievable or hardly
achievable) of the uncomplexed ion. This condition is, however,
in practice only rarely fulfilled and, even for the less polarizable Ng atoms, the simple perturbation of the symmetry of
the ion can influence the spectroscopic selection rules and
change its intrinsic IR spectrum. As a matter of fact, it is
commonly observed that the Ng atom(s) interact with the
ion and influence its IR spectrum. Therefore, the Ng-tagging
technique also furnishes information on the extent and the
character of cations–noble gas interaction. For example, in
the above-mentioned experiments,107,108 the M+(H2O)(Ar)n or
M2+(H2O)(Ar)n (M = Mn, Sc; n ≤ 7) produced by a pulsed-nozzle
laser vaporization cluster source are mass selected by a ToF
mass spectrometer and then excited with an IR laser in the
O–H stretching region. This promotes the loss of Ar atoms and
the formation of fragment ions whose intensity is recorded as
a function of the IR frequency. Based also on DFT calculations,
the experiments revealed a clear influence of the number of
Ng atoms on the absorption frequencies and furnished details
about the structure and stability of the solvation shells around
M+(H2O) and M2+(H2O). For Sc+(H2O)Ar, the partially resolved
rotational structure showed, in particular, that the H–O–H
bond angle is larger than it is in the free water molecule.
What about the interaction of noble gases with metal anions?
In general, passing from cationic to anionic species, the
stability of the corresponding complexes with the noble gases
drastically reduces and it is not surprising that the observed
complexes of Ng atoms with metal anions are considerably
less numerous than those observed with metal cations. The
weakness of the M–∙Ng interaction is clearly appreciated, for
example, by inspecting the theoretical data, listed in Table 6,
very recently computed for the complexes of Cu–, Ag– and Au–
with He, Ne and Ar.111 The diatomic Au– Ar had previously been
observed112 using photoelectron spectroscopy. The comparison with the spectrum of the naked Au– revealed a weak
interaction between Au– and Ar, quantitatively appreciated as
ca. 3.8 kJ mol–1 by theoretical calculations.112 All the Au–∙Ng
(Ng = Ne, Ar, Kr, Xe) were also theoretically compared112 and
the predicted Au–/Ng interaction energies were found to regularly increase from 0.6 kJ mol–1 to 9.0 kJ mol–1 passing from
Au–∙Ne to Au–∙Xe. This trend parallels the regular increase in
the polarizabilities of the Ng atoms passing from Ng = Ne to
Ng = Xe (see Table 1). The complexes of the cluster anions Aun–
with Ar atoms have also been reported recently113,114 and the
electronic photodissociation spectroscopy of Aun–∙Xe (n = 7–11)
has previously been investigated.115
Complexes with non-metal cations: stability
and structural motifs
The simplest complexes of the noble gases with non-metal
cations are the diatomic NgH+ (Ng = He–Xe). Their dissociation channel of lower energy is the loss of H+, whose thermo­
chemistry is measured by the PA of Ng, namely the minus
enthalpy change of the reaction Ng + H+ ® NgH+. The only
432
Review of Gas-Phase Chemistry of Noble Gases
Table 6. Theoretical bond distances (Re), dissociation energies (De), and harmonic vibrational frequencies (ωe) of the complexes of He, Ne,
and Ar with the coinage metal anions Cu–, Ag– and Au– (taken from Reference 111).
M–
Ng
Re
(Å)
De
(kJ mol–1)a
we
(cm–1)
Cu–
He
 6.61
 0.05
 6
Ne
 5.00
0.4
10
Ar
  4.49
2.4
20
He
 6.40
0.1
 7
Ne
5.0
0.4
10
Ar
 4.53
2.5
19
Ag–
Au
a
–
He
 5.03
0.2
Ne
 4.33
0.8
Ar
 4.11
4.0
16
17
112
27
Depth of the potential well with no ZPE
Figure 1
He
Ne
Ar
Kr
Xe
1.235
1.381
1.641
1.807
2.048
He
Ne
Ar
Kr
Xe
1.060
1.057
0.997
0.935
0.864
Ar
Ar
Ar
Ar
1.811
2.100
0.946
2.009
0.889
0.870
0.945
0.823
Ar
Ar
Ar
Ar
3.089
3.056
Ar
Ar
2.107
0.885
Ar
2.115
Ar
0.883
Ar
Ar
Ar
Figure 1. Theoretical connectivities and non-equivalent bond distances (Å) of (NgH)2+ and H3+(Ar)n (n = 1–5) (data from References 118
and 126).
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)433
Table 7. Energy changes for the loss of Ng atoms from NgH+, (NgH)2+, and H3+∙Ng (kJ mol-1) (see also Figure 1).
Species
NgH
+a
(NgH)2+ b
+
H3 ∙Ng
He
Ne
Ar
Kr
Xe
177.8
198.8
369.2
424.6
499.6
23
55
209
278
376
c
1.7
4.6
d
30.8
d
28.0
e
56.5
d
98.9d
a
Experimental PA taken from Reference 72
Theoretical energy change at 0 K of the reaction Ng–H–H–Ng+ ® H2+ + 2Ng taken from Reference 118
c
Theoretical value taken from Reference 124
d
Theoretical value taken from Reference 127
e
Experimental value taken from Reference 123
b
exception is XeH+, whose dissociation limit of lower energy is
Xe+ + H (the IE of H, 13.6 eV,72 is higher than Xe). The diatomic
NgH+ are quite stable in the gas phase and have been well
known for a long time.116,117 It is of interest that recent theoretical calculations118 predicted the somewhat unexpected
existence of the dimeric ions (NgH)2+. These species possess
the linear symmetric structures shown in Figure 1. Similar to
the other radical cations [HnE–H–H–EHn]+ (EHn = hydrides of
elements of groups 15–17) investigated in the same study,118
the (NgH)2+ dimers must be viewed as adducts between H2+
and two Ng atoms. The alternative description as electronbound dimers of two NgH+ was discarded by energy ­arguments
and by bonding analysis. The average dissociation energies
per Ng atom derivable from the data listed in Table 7 are relatively large and arrive up to 188 kJ mol–1 for (XeH)2+. The stability of the Ng–H–H–Ng+ cations is, however, limited by their
rearrangement into the Ng---NgH2+ isomeric structures. This
process is exothermic for Ng = Xe and occurs with negligible
barriers for Ng = He and Ne. It was therefore suggested to limit
the experimental hunt to the argon and krypton cations. 118
However, the attempted ionization of Ng/H2 mixtures under
CI conditions118 did not produce any detectable Ar2H2+ and
Kr2H2+. It is of interest that it was possible, instead, to observe
the lightest He2H2+ by EI of helium droplets doped with H2.119
MIKE spectrometry not only revealed the expected dissociation of He2H2+ into HeH2+ and He with a low KER of 15 ± 4 meV,
but also the somewhat unexpected dissociation into HeH +
and HeH (or He + H), which occurs with higher probability and
whose KER is four-times larger than that of the loss of He.
These experimental findings are reconciled with the predicted
fragility of the ground state He–H–H–He+ with respect to the
loss of He atoms by assuming the formation of a metastable
electronically excited He2H2+. The excess energy stored in the
system as a result of the ionization event allows the rupture
of the strongest H–H+ bond, while the weaker He–H+ remains
intact. These findings stimulate further theoretical studies on
the electronic structure and dynamics of the excited states of
the Ng2H2+ cations.
The conceivable sequestration of the noble gases by H3+ in
planetary objects120 has also recently rejuvenated the interest
for the H3+(Ng)n complexes (Ng = He–Xe, n ≥ 1), investigated so
far by experimental and theoretical methods.121–125 “State-of
the-art” ab initio126–128 and DFT calculations129 have been, in
particular, performed to investigate the structure, stability
and spectroscopic properties of various H3+(Ng)n (Ng = Ne–
Xe; n = 1–5). As suggested previously,124,125 these complexes
consist of a H3+ ionic core surrounded by Ng atoms. Figure
1 shows, in particular, the predicted geometries 126 of the
exemplary argon cations. The clusters with up to three noble
gases possess planar structures, with the ligands attached
to the apices of the H3+ equilateral triangle. For Ar–H3+, the
apex-coordination is also supported by spectroscopic measurements,121,122 refined until recently.130 The fourth and the
fifth Ng atoms sit, instead, in axial positions above and below
the equatorial plane and H3+(Ar)6 is predicted to be a regular
octahedron.125 As shown in Table 7, the complexation energies
of the singly-coordinated H3+∙Ng periodically increase from
H3+∙He to H3+∙Xe and range, in particular, from 1.7 kJ mol–1 to
98.9 kJ mol–1.124,127 The calculations also revealed127 that the
structure of H3+∙Ng gradually changes from practically pure
H3+∙He and H3+∙Ne to a situation close to XeH+–H2. This reflects
the fact that the PA of H2, 422.3 kJ mol–1,72 is lower than the
PA of Xe (see Table 7). Therefore, the periodic increase in the
stabilities of the H3+∙Ng with respect to the loss of Ng reflects
not only the increase in the polarizability of the noble gas (with
consequent increase in the charge transfer from Ng to H3+),
but also the onset of covalency in the Kr–H and especially in
the Xe–H interaction. It is also of interest to note from Table
7 that, for any Ng, the H 3+∙Ng complex is, in general, less
stable (with respect to the loss of Ng) than the corresponding
NgH+ and Ng2H2+ and that the complexation energies per Ng
atom decrease in the order H+ < H2+ < H3+. Passing from H+ to
H3+, the positive charge is progressively more delocalized and
the extent of the interaction with the Ng atom progressively
reduces. This “size effect” on stability is indeed typical of other
series of noble gas complexes with non-metal cations. It is
finally of interest to note that, for the H3+(Ng)n (n ≥ 2), the most
recent calculations126,128,129 confirm that the binding energy
of the nth atom, namely the energy change of the reaction
H3+(Ng)n ® H3+(Ng)n–1 + Ng, tends to decrease by increasing n.
Appreciable jumps are, in particular, predicted between n = 1
and n = 2 and between n = 3 and n = 4. These theoretical trends
434
Review of Gas-Phase Chemistry of Noble Gases
are consistent with the decreasing values of 28.0 kJ mol–1
the He atoms at nearly equivalent distances from the two Z
(n = 1), 19.1 kJ mol–1 (n = 2), 17.9 kJ mol–1 (n = 3), 10.3 kJ mol–1
moieties and Z–He bond lengths that are invariably longer
(n = 4), 9.5 kJ mol–1 (n = 5), 9.1 kJ mol–1 (n = 6) and 6.5 kJ mol–1
than the corresponding values of the monomeric Z+∙He. It is of
123
(n = 7) measured so far for the Ar series.
interest that the (NO)2+He exists in a cis and in a slightly more
+
In addition to H2 (He)2, various novel and somewhat unex- stable trans conformation.
pected complexes of helium atoms with non-metal cations
The noble gas-tagging technique 109,110 mentioned in the
were recently obtained from the ionization of helium nano- previous paragraph has recently been employed to investigate
droplets doped with molecular species.131–133 Before these
the IR absorptions of various non-metal cations.136–145 It is
investigations, the attachment of helium atoms to ions from
first of interest to mention the “Eigen” (H3O+) and the “Zundel”
dopant molecules had only rarely been observed. For example, (H2O–H–OH2+) cations, the two limiting forms of proton accomNO+(He)n (n = 1–15) which had so far been detected by ionizing
modation in water. The relative weight of these two ions essenhelium droplets doped with NO 134 and CH 3+(He) n (n = 1–3), tially depends on the number of solvating water molecules
CH4+(He)n and N2+(He)n (n = 1, 2) were observed from droplets
and this stimulates considerable interest for the structure and
doped with CH4, D2 and N2.135 Using dopants such as SF6, CCl4, stability of H+(H2O)n clusters of variable size. The Ng-tagging
C6H5Br, I2 and CH3I, it was possible, instead, to observe131,132
technique has, in particular, been employed to investigate the
helium attachment to numerous monoatomic and polyatomic
IR spectra of the gaseous H+(H2O)n (n ≥ 1) solvated by a varications, including F+, SFn+ (n = 1, 2, 5), Cl+, Cl2+, CCln+ (n = 2, 3), able number of Ng atoms (especially argon).136–141 Signature
C2Cl7+, Br+, I+, I2+, I3+, CH3I+ and CH3I2+. Even though the anal- bands of clusters that contain up to 11 water molecules were
ysis of the data was sometimes limited by the congested char- detected and the spectra were discussed in terms of the relaacter of the spectra, for most of the X+(He)n ion series it was
tive contributions of the Eigen and Zundel limiting forms. In the
possible to observe a stepwise drop in the ionic distribution at
present context, it is of interest to recall the salient information
some magic value n*, which suggested the closure of the first
derived from these studies about the character and the extent
solvation shell. In particular, for the monoatomic F+, Cl+, Br+
of the interaction of Ng atoms with the hydrated proton. Thus,
and I+, the n* showed an increasing trend passing from F+ to
the IR spectra of H5O2+∙Ne138,140 indicated that the symmet+
132
I and ranged from nearly 10 to nearly 16–17. It is of interest
rical Zundel ion remains essentially intact in the complex and
that, based on a simple classical model, the observed n* were
this confirms the general behavior of Ne as a weak solvating
employed to estimate the ionic radii of the cations as 1.80 Å
ligand. On the other hand, the spectra of the H5O2+(Ar)n138–140
+
+
+
+ 132
(F ), 1.98 Å (Cl ), 2.27 Å (Br ) and 2.63 Å (I ). The helium affini- generally exhibit complex band structures that reflect solventties of various X+ were also estimated as the ratio of the sum of
induced symmetry breaking of the Zundel core ion. To evaluate
the ion yields of all ions X+(He)n (n ≥ 1) and the yield of the bare
the extent of solvent perturbation, theoretical calculations
ion X+,131 and were found to be non-linearly dependent on the
were, in particular, performed on the simplest H5O2+∙Ar and
+
number of atoms of X . The largest values were, in particular, H5O2+(Ar)2.138 The predicted structures of these ions, shown in
obtained for the atomic F+ and Cl+.
Figure 3, revealed a distinct tendency of the Ar atoms to attach
The electron ionization of helium droplets doped with N2, O2, to the spectator OH groups of H5O2+ rather than to the shared
CO and NO133 produced various He-solvated cations. The most
proton. In the asymmetrically-solvated complexes, the shared
interesting and somewhat surprising result was that, while
proton resides closer to the more heavily solvated water molethe monomer species (with the exception of NO+) show little
cule and this leads to red-shifts in the Ar-solvated stretches
tendency to capture and retain He atoms on their journey out
and to blue-shifts in the shared proton vibrations. In particof the droplet, the cluster cations (N2)m+, (O2)m+, (CO)m+ and
ular, based on the observed spectral shifts, the conclusion
(NO)m+, with m ≥ 2, all show a distinct affinity for helium and
was reached138 that the H5O2+(Ar)2 isomer of lowest energy
+
form the corresponding (Z)m (He)n cluster ions. Ab initio calcu- is that with two Ar atoms attached to each of the H atoms on
lations also revealed133 that the helium binding energies of any
the same water molecule. The appreciable effect of solvating
(Z)2+∙He were invariably lower than the monomeric Z+∙He, thus
Ar atoms on the IR spectra of the H+(H2O)n clusters is not
suggesting that the observed preferential attachment of He to
unexpected. For example, in the simplest H3O+∙Ar, the binding
+
the polymeric (Z)m does not simply reflect thermochemical
energy is as large as 21.5 kJ mol–1146 and yields substantial
factors. The different behavior of the monomer and the cluster
rearrangement of the H3O+ ionic core.146 It is, however, generions was, instead, explained by a more efficient cooling of
ally accepted that, even though the Ng atoms are not totally
the (Z)m+(He)n clusters following the initial ionization event.133 “innocent” messengers, they do not alter the intrinsic strucThis is, in particular, attributed to two factors, namely the
tural motif of a given H+(H2O)n. It is of interest that very recent
+
evaporative loss of monomers from larger (Z)m and a more
results on the H+(H2O)6(Ng)n complexes (Ng = Ne, Ar, Kr, Xe)141
effective channeling of excess energy into the helium matrix, revealed a messenger-dependent balance in this cluster
most likely through the intermolecular vibrational modes of
between the H3O+ and H5O2+ core isomers. The H+(H2O)6 is the
lower frequency that are available in the clusters but not in
smallest system in which both the Eigen and Zundel motifs
the monomers. It is also of interest to inspect the predicted
co-exist. The bare H+(H2O)6 was assigned as a mixture of the
geometries, shown in Figure 2, of the dimeric (Z)2+He. These
Eigen and Zundel motif,147 while H+(H2O)6∙Ar was assigned as
ions possess symmetric or nearly symmetric structures, with
the Zundel type isomer.139 The IR spectra of the H+(H2O)6(Ng)
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)435
113
F
He
He
2.905
2.905
2.651
105.8
178.9
N
2.014
N
N
1.121
N
1.109
N
N
1.109
He
He
2.815
2.718
3.264
78.5
O
O
O
O
1.122
114.6
1.164
O
2.153
112.7
1.164
O
He
2.912
He
2.476
125.4
O
C
1.138
O
C
1.112
2.993
143.3
O
1.138
1.533
143.5
C
He
He
He
2.945
2.945
2.731
2.856
88.8
O
N
N
1.065
1.110
O
2.252
103.4
103.4
2.856
N
N
1.110
O
118.8
1.109
O
118.8
2.226
1.109
N
O
Figure 2. Theoretical connectivities and main geometrical parameters (distances in Å and angles in degrees) of Z+∙He and (Z)2+∙He
(Z = N2, O2, CO and NO) (data from Reference 133).
114
436
Review of Gas-Phase Chemistry of Noble Gases
Figure 3
Ar
2.309
1.093
Ar
1.345
1.121
2.311
1.299
2.303
Ar
Ar
2.355
1.198
1.205
1.201
2.354
Ar
Ar
1.201
1.201
2.355
Ar
2.363
2.362
1.201
Ar
2.362
Ar
Figure 3. Theoretical connectivities and main bond distances (Å) of H5O2+∙Ar and H5O2+(Ar)2 (data from Reference 138).
revealed141 that, while the Ar- Kr- and Xe-mediated absorptions are mainly consistent with the Zundel isomer (theoretically predicted to be more stable than the Eigen isomer by
3.9 kJ mol–1), the Ne-mediated spectra are accounted for by a
mixture of the two motifs. The theoretical messenger spectroscopy, recently applied to study the solvation of H+(H2O)n by
H2 molecules,148 could certainly help to reveal further details
on the structure and stability of the H+(H2O)6(Ng)n complexes,
and, in general, to help the interpretation of the results from
Ng-tagging spectroscopy. In any case, the recent investigation
of the infrared spectra of the complexes of alkali metal ions
with water,142 tryptamine,143 and crown ethers,144 also revealed
the Ar-induced trapping of the high-energy conformers of
some of the investigated ionic species.
In the last decade, the IRPD spectroscopy has also been
extensively used to investigate the complexes of the noble
gases, especially helium, neon and argon, with organic
cations. Extensive data have been produced by Dopfer and his
co-workers in particular, who investigated systems that range
from the simplest CH3+ to larger substituted aromatic cations.
The experimental results are invariably supported by ab initio
or DFT calculations and detailed accounts of exemplary results
had already been reported in review articles.109,146,149 At ­variance
with the above-mentioned applications of the Ng-tagging technique,136–145 more emphasis is placed in these studies on the
n
ion–ligand interactions and bonding motifs. A good recent illustrative case is the complexes of Ar with protonated benzaldehyde (BZH+).150 The BZH+ and its argon complexes BZH+∙Ar
were produced by CI in a pulsed supersonic plasma expansion.
The IRPD spectrum of BZH+ indicated the presence of the cis
and trans isomers of the oxonium ion (the former is theoretically predicted to be more stable by nearly 10 kJ mol–1), with
no signature of the significantly less stable carbenium ions
arising from ring protonation. The theoretical calculations also
predicted the formation of four distinct isomeric BZH+∙Ar, whose
optimized structures are shown in Figure 4. The global minima
are the H-bonded structures 1a–Ar(H) and 1b–Ar(H), whose
intermolecular Ar–HO bonds are characterized by dissociation
energies of 8.2 kJ mol–1 and 7.1 kJ mol–1, respectively. Isomers
1a–Ar(p) and 1b–Ar(p) are instead local p-bonded minima, with
argon binding energies which are lower by 2–3 kJ mol–1 than
those predicted for the H-bound global minima. The stability
of the various isomers decreases in the order 1a–Ar(H) > 1b–
Ar(H) > 1b–Ar(p) > 1a–Ar(p) and all the isomers are predicted
to be formed in the molecular beam. It is of interest that the
three isomers 1a–Ar(H), 1a–Ar(p) and 1b–Ar(H) could, indeed,
be clearly distinguished by c­ haracteristic wavenumbers and
band shapes of their O–H stretching frequencies. In addition, even though spectral congestion prevented a quantitative d
­ etermination of the relative abundance of the individual
115
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)437
Figure 4
Ar
176.0 O
Ar
3.51
2.22 H
O
H
1a-Ar(H)
105.0
1a-Ar(π
π)
Ar
Ar
2.34
153.0
3.51
H
H
O
105.0
O
1b-Ar(H)
1b-Ar(π
π)
Figure 4. Theoretical connectivities and main geometrical parameters (distances in Å and angles in degrees) of the complexes of Ar
with protonated benzaldehyde (data from Reference 150).
BZH+∙Ar, it was possible to guess a significantly larger abundance of 1a–Ar(H) with respect to 1b–Ar(H).
Finally, it is of interest to mention here recent theoretical studies on the “inserted” noble gas–non metal cations
HNgCO+,151 and HNgYNgH+ (Ng = He–Xe; Y = H, F).152,153 These
species are the cationic counterparts of the neutral HNgY and
HNgYNgH (Y = electronegative atom or group), the “cold” noblegas molecules that have attracted considerable experimental
and theoretical interest over the last decade.2,15,16 Figure 5
shows all the HNgCO+ and HNgYNgH+ that are predicted to be
energy minima. These species possess linear structures, with
Ng atoms formally inserted into a H–Y bond (Y = C, H, F).
The detailed analysis of charge distributions and bonding
properties revealed, in particular, that the HNgCO+ must be
viewed as ion–dipole complexes between HNg+ and CO. The
HNgYNgH+ are, instead, best formulated as (H–Ng+)2X– (X = H,
F), namely ion–dipole complexes between a central H– or F–
and two covalent HNg+. This description is consistent with
previous theoretical results on HXeHXeH +154,155 and closely
resembles the typical formulation of the neutrals HNgY as
(HNg+)Y–.15,16 It is of interest that the xenon cation HXeFXeH+ is
116
isoelectronic with the experimentally observed HXeOXeH.156 As
for thermochemical stability, all the HNgCO+ and HNgYNgH+,
in general, reside in high-energy regions of the corresponding
Figure 5
C
0.764
0.967
1.281
1.417
1.610
He
Ne
Ar
Kr
Xe
2.221
2.712
2.911
2.968
3.124
O
1.128
1.130
1.129
1.129
1.130
F
0.749 He
0.977 Ne
1.281 Ar
1.424 Kr
1.610 Xe
1.594 He
2.085 Ne
2.193 Ar
2.250 Kr
2.345 Xe
1.381 Ar
1.515 Kr
1.687 Xe
1.987 Ar
2.014 Kr
2.119 Xe
Figure 5. Theoretical connectivities and non-equivalent bond distances (Å) of HNgCO+ and HNgXNgH+ (X = H, F) (data from References
151 to153).
438
Review of Gas-Phase Chemistry of Noble Gases
potential energy surfaces and are less stable than decomposition channels that involve the formation of highly stable
ionic and neutral products such as HCO+, H2 and HF. However,
especially for the HNgCO+ and HNgFNgH+ cations that contain
Ar, Kr and Xe, these decompositions pass through transition
structures of relatively high energy and, overall, these ions
are predicted to be metastable and, in principle, observable
under suitable experimental conditions.151–153 On the other
hand, only HXeHXeH+ resulted in being metastable,152,154 while
both HArHArH+ and HKrHKrH+ were, overall, predicted to
be unstable even at the lowest temperatures.152 It is also of
interest to note that the HNgHNgH+ cations (Ng = Ar, Kr, Xe) are
considerably less stable than H3+(Ng)2 isomeric clusters such
as those shown in Figure 1. They are, therefore, not expected
to play a role in the sequestration of noble gases by H3+ in
protoplanetary objects.120
Complexes with non-metal anions: searching
for covalent structures
The complexes of the noble gases with non-metal anions (indicated here as X–) typically consist of weakly-bound van der
Waals adducts. The interaction of X– with Ng atoms does not,
in fact, produce an effective overlap of the electronic distributions. Rather, the X–/Ng potential wells are essentially dominated by charge-induced dipole interactions and, even for the
most polarizable krypton and xenon, these long-range forces
are generally weak. Therefore, the anionic complexes of the
noble gases, typically, feature long bond distances and low
dissociation energies. This fragility is clearly appreciated, for
example, by examining the properties of the diatomic X–∙Ng
(X– = F–, Cl–, Br–, I–, O–, S–), also extensively investigated with
unceasing interest in the last decade.157–174 The accurate theoretical data recently reported for the halide complexes are
listed in Table 8.
Even for the most stable F–∙Xe (apart from the hardly accessible F–∙Rn), the bond distance is nearly 3.0 Å long and the dissociation energy is lower than 30 kJ mol–1. In comparison, this
value is only twice that of the dissociation energies of Fr+∙Xe
and Ra+∙Xe, which are the least stable among the alkali- and
alkaline–earth cations/noble gas complexes59–66 (see Tables 2
and 3). It is also evident from Table 8 that, for any X–, the dissociation energies of the complexes periodically decrease passing
Table 8. Theoretical bond distances (Re), dissociation energies (De), and harmonic vibrational frequencies (ωe) of the complexes of the noble
gases with the halogen anions (taken from References 157 and 160).
X–
F–
Cl–
Br
–
I–
a
Depth of the potential well with no ZPE
Ng
Re
(Å)
De
(kJ mol-1)a
we
(cm-1)
He
3.26
 0.9
 42
Ne
3.14
 2.2
 49
Ar
3.02
10.5
 93
Kr
2.99
16.4
104
Xe
2.96
26.7
123
Rn
2.94
33.6
135
He
3.96
  0.5
 26
Ne
3.74
 1.4
 31
Ar
3.67
 6.2
 54
Kr
3.72
 9.3
 57
Xe
3.70
14.2
 64
Rn
3.68
17.6
 68
He
4.24
 0.4
 25
Ne
3.97
 1.2
 25
Ar
3.91
  5.2
 40
Kr
3.91
 7.8
 39
Xe
3.95
11.7
 42
Rn
3.92
14.6
  43
He
4.51
  0.5
 26
Ne
4.25
 1.1
 22
Ar
4.16
 4.6
 34
Kr
4.17
 7.3
 32
Xe
4.20
11.1
 34
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)439
from Xe to the lightest congeners and one notes, in particular,
the remarkably low stability of the X–∙He and X–∙Ne. Comparably
low stabilities are also predicted for the helium and neon
complexes of O–,167,168 and S–.173,174 Consistently, using conventional cluster-ion sources, only anionic clusters of Ar, Kr and Xe
are observed and these systems have already been extensively
investigated by various spectroscopic and theoretical methods
(see for example, References 175–191). It is of interest that
working at the exceptionally low temperatures of the helium
droplets, it has recently been possible to observe the attachment of He atoms to a variety of anionic species.132,192–195 The
simplest X–(He)n clusters (X– = F–, Cl–, Br–) with n up to 25 were
detected by ionizing helium droplets doped with SF6, CCl4 and
C6H5Br.132 As with their cationic analogs, X+(He)n, reported in the
same study132 and discussed in a previous paragraph, each ion
series X–(He)n exhibits a stepwise drop in the ionic distribution
at some magic value n*, which suggests the closure of the first
solvation shell. The n* are invariably larger than those obtained
for the corresponding cations and derived, in particular, as
18.3 ± 0.9 for F–, 19.5 ± 0.2 for Cl– and 22.0 ± 0.2 for Br–. These
values were employed to estimate the ionic radii of the anions
as 3.07 Å (F–), 3.14 Å (Cl–) and 3.46 Å (Br–). While these estimates
are, on average, nearly a factor of two larger than those derived
from alkali halide crystals,196 they are instead consistent with
other experimental and theoretical estimates of the radii of
the halide anions in superfluid helium.197–199 Variational and
diffusion Monte Carlo calculations have also been employed
to determine radial density profiles and solvent evaporation
energies for X–(He)n (X– = F–, Cl–, Br–, I–) with n up to 40 (41 for
I–).199 While the X–∙He interactions are generally weak (see Table
8), they are still large enough to cause solvation. This is in
contrast, for example, to H–, which is even more weakly bound
to He200 and remains outside the helium cluster.201 Around the
halide anions, the solvent forms a very delocalized layer, with
permanence of the liquid-like quantum features of the solvent
atoms surrounding the anionic impurities. This is in contrast to
the more structured, solid-like behavior of the quantum solutions with metal cations embedded in He droplets.43–53 Overall,
in superfluid helium, the halogen anions are best viewed as
remaining solvated within liquid-like solvent bubbles, the size
of which is dependent on the embedded species. In particular,
the theoretical results by Coccia et al.199 were extrapolated by
Ferreira da Silva et al.132 so to estimate the size of the cavities
as 2.7 Å (F–), 3.3 Å (Cl–) and 3.5 Å (Br–). For F– and Cl–, values of
2.67 Å and 3.02 Å, respectively, were previously obtained from ion
mobilities in superfluid bulk helium.197,198
Helium atoms also attach to the anionic clusters of water,192
acetic acid,193 and formamide.194 Even more interesting is the
observation of helium attachment to the anionic clusters of
glycine (Gly), alanine (Ala) and serine (Ser).195 These results,
in fact, open up exciting perspectives in the study of the still
little explored interaction of Ng atoms with ionic species of
biological interest. The ionization of helium droplets doped
with Gly, Ala and Ser promotes, in particular, the attachment
of He atoms to their parent anions clusters Gly2–, Ala2– and
Ser2–. The most prominent complexes are those formed with
the glycine dimer anions and it was possible to observe Gly2–
(He)n with n up to at least 18. Helium clusters were also seen
with the dehydrogenated dimer anion (Gly2–H)– but, compared
with Gly2–(He)n, the intensities of these complexes are lower
than the intensity ratio of the bare (Gly2–H)– and Gly2–. This
was taken195 as an indication of substantial differences in the
electronic structures of the two anions, with Gly 2– offering
a more attractive binding environment for He atoms. It is of
interest that the Gly2–(He)n clusters show a very prominent
magic number at n = 8 and there is also an indication of a shell
closure at n = 16. Helium atoms were also seen attached to
Ala2–, (Ala2–H)– and Ser2–, but, when compared to the systems
comprising Gly2– and (Gly2–H)–, these complexes are considerably less intense than the He-free parent anions. It is of
interest that no addition of He atoms was observed to the
monomer anions Gly–, Ala– and Ser– and only (Gly–H)– showed
a very little tendency to complexation. These experimental
findings invite theoretical work to throw light on the detailed
aspects of the interaction of helium atoms with polyatomic
anionic species.
The overall fragility of the complexes of the noble gases with
gaseous anionic species stimulates questions concerning the
conceivable existence in the gas phase of more compact covalent structures. An example of this is XeF3–, which has so far
been detected in the negative ion mass spectrum of XeF2,202
recently obtained in the gas phase from the direct association of F– to XeF2.203 XeF3– and also recently been detected
in solution as the intermediate involved in the fluoride
exchange reaction of XeF2.204 Based on energy-resolved CID
experiments, the fluoride ion affinity of XeF2 was measured
as 0.84 ± 0.06 eV (81.1 ± 5.8 kJ mol–1).203 This value is certainly
higher than the dissociation energy of F–∙Xe (see Table 8) and
suggests a tighter interaction between xenon and fluorine.
Theoretical calculations confirmed, in fact,203,204 that XeF3– is
best described as a complex between F – and XeF2, with a
F–---XeF2 bond distance of 2.4 Å and a weak covalent ion–
neutral interaction. This species is, however, definitely less
stable and structurally less compact than the xenon covalent anions observed in the condensed phase.14,205–209 The
pentacoordinated XeF5–, in particular, is a covalent species
of D 5h symmetry, with short Xe–F distances of 2.012 Å. 205
Consistently, the F– affinity of XeF4 is theoretically estimated
to be as large as 247.3 kJ mol–1.209 In any case, the observation of the borderline species, XeF3–, encourages the experimental search of novel covalent xenon anions that are stable
in the gas phase. Two recent theoretical candidates are the
NXeO2– and NXeO3– shown in Figure 6.210 These two species
were characterized as true minima on the singlet surface and
the best estimates of their atomization energies were nearly
200 kJ mol–1 and 400 kJ mol–1, ­respectively. In addition, even
though they resulted in being thermo­chemically unstable
with respect to various ­dissociation ­channels, the barriers
of these unimolecular dissociations were estimated to be at
least 170 kJ mol–1. These values are, indeed, large enough
to support the prediction that both NXeO2– and NXeO3– could
exist as metastable (kinetically stable) species. The most
117of Noble Gases
Review of Gas-Phase Chemistry
440
Figure 6
N
N
113.2
1.825
Xe
1.860
115.9
1.800
Xe
1.810
O
101.9
O
O
102.4
O
1.626
2.241
2.259
2.321
He
Ar
Kr
Xe
O
S
1.793
2.318
2.300
2.337
He
Ar
Kr
Xe
F
1.566
2.246
2.333
2.466
F
He
Ne
Ar
Kr
Xe
1.725
2.236
2.293
2.311
2.349
1.203
1.573
1.820
1.967
2.153
Se
1.859
2.353
2.327
2.346
B
O
1.627
Ar
O
F
1.110
1.781
1.854
1.967
O
1.462
Ar
1.602
O
F
N
115.3
N
O
1.266
1.272
1.270
1.271
1.274
O
1.737
1.733
Ar
Ar
Ar
2.360
F
2.437
F
Ar
Ar
F
O
1.736
2.389
2.477
2.612
N
O
1.730
He
Ar
Kr
Xe
2.499
Ar
O
Ar
O
Ar
Ar
O
O
O
O
1.748
O
Ar
1.742
O
Ar
O
Ar
2.615 Ar
F
O
2.547
F
Ar
O
O
O
Ar
2.573
Ar
Ar
1.744
Ar
Ar
O
Ar
O
O
Figure 6. Theoretical connectivities and main geometrical parameters (distances in Å and angles in degrees) of covalent noble gas
anions (data from References 210 to 214 and 216).
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)441
interesting structural feature of the two anions is the Xe–N
bond distance, predicted to be only 1.8 Å. As discussed in the
subsequent paragraph, the lengths of single Xe–N bonds
typically range around 2.0–2.1 Å. Also taking into account the
calculated Lewis structures, the Xe–N interactions of NXeO2–
and NXeO3– were tentatively assigned as triple bonds.210 The
NArO3– and NKrO3– were also predicted to reside in potential
energy wells, but they both resulted in being less stable
(especially NArO 3–) than NXeO 3–. 210 The metastability of
NArO3– was actually anticipated nearly ten years ago211 and
the conceivable existence of the fully planar NArN2– was also
noticed.211 As shown in Figure 6, both NArO3– and NArN2–
possess short Ar–N and Ar–O bond distances and they are,
indeed, first predicted examples of anions of the lighest noble
gases with compact covalent structures. This family of theoretical species has, more recently, been expanded to include
the discovery of covalently-bound anions containing helium
and neon.212–218 These species are shown in Figure 6. The
first investigated systems were the linear FNgO– (Ng = He, Ar,
Kr),212 located as deep-energy minima on the singlet potential energy surface. These anions are thermochemically
stable with respect to the dissociation limit F– + Ng + O(1D)
and protected by high-energy barriers with respect to the
exothermic decomposition into FO – and Ng. The dissociation of FKrO – into F – + Kr + O( 3P) is also endothermic, but
the corresponding dissociations of FHeO – and FArO – are
exothermic. However, for both these species, the energies
required to cross from the singlet FNgO– (Ng = He, Ar) to the
triplet dissociation limit are large enough (30–45 kJ mol–1)216
to support the prediction that they can exist as metastable
species. It is of particular interest to note that the singlet
FNgO– possess rather short F–Ng and Ng–O bond distances
(see Figure 6). This finding is highly surprising, if one thinks
of the fragility of the diatomic F–∙Ng (see Table 8) and to the
fact that the diatomic NgO (Ng = He, Ar, Kr) are unbound or
only marginally bound. The tight compactness of the FNgO–
indeed reflects a novel and somewhat unexpected structural motif, namely the ability of F– to induce the formation of intrinsically unstable NgO bonds and the subsequent
formation of an ion–dipole complex, best described by the
resonance form F –---(Ng–O). Detailed analyses of charge
distributions and bonding properties revealed that,212,217 even
for FHeO–, the Ng–O bond is covalent and polar, while the
F–---Ng interaction is essentially electrostatic.
The discovery of the metastable FNgO– stimulated further
theoretical work on various related anionic species. 213–218
Based on the speculation that a single fluoride ion could
induce the simultaneous formation of more than one Ng–O
bond, the poly-coordinated anions, F–(NgO)n (Ng = He, Ar, Kr;
n = 1–6), were theoretically explored213 and highly-symmetric
structures such as the exemplary argon anions shown in
Figure 6 were actually located as true energy minima for any
Ng. It is of interest that even though the overall stability of
these complexes tends to decrease by increasing the number
of coordinated NgO groups, these large-size anions essentially retain the compactness of the simplest FNgO –. The
conceivable existence of the group XVI-congeners, FNgX –,
was also theoretically investigated (Ng = He–Xe; X = S, Se).214–
216
With the exception of FNeX– (X = S, Se), these anions were
invariably characterized as true energy minima, even though
the energy barriers and crossing points that protect them from
the exotermic decomposition into FX– + Ng and F– + Ng + X(3P)
periodically decrease from FNgO– to FNgSe–. Thus, all the
sulphur anions FNgS– (Ng = He, Ar, Kr, Xe) were predicted
to be metastable, but only FKrSe– and FXeSe– resulted in
being kinetically stable. These species are indeed interesting
examples of molecular species with Ng–S and Ng–Se bonds.
Stimulated by the idea that the fluoride anion could stabilize
elusive complexes of the noble gases with polyatomic species,
noble gas anions with the general formula FNgBN– (Ng = He–
Xe) were theoretically explored218 (see Figure 6). All these
species, including FNeBN– (one of the few predicted molecular species containing neon), were located as true minima
on the singlet surface and found to be thermodynamically
stable with respect to the loss of F, F–, BN and BN–. These
anions are unstable with respect to Ng + FBN– but, at least for
Ng = Ar, Kr, Xe, the involved energy barriers are high enough
to suggest their conceivable metastability. As with the FNgX–
(X = O, S, Se), the compactness of the FNgBN– arises from the
strong F– stabilization of the intrinsically unstable NgBN. The
character of the boron–noble gas bond passes from purely
ionic for FHeBN– and FNeBN– to covalent for FXeBN–.218 The
ability of anions other than F– to stabilize noble gas elusive
molecules was also investigated by exploring the stability of
ClHeO– and HOHeO–.217 At the highest levels of theory, only
the former species turned out to be a local minimum, even
though the He–O bond of Cl–---(HeO) resulted in being much
weaker than its lighter homologue F–---(HeO). In conclusion,
the theoretical calculations highlight the fact that, in the
presence of suitable anionic species (for example, F–), it is
possible to enhance the stability of intrinsically unstable
chemical bonds involving Ng atoms, up to the formation of
covalent species. Searching for suitable conditions for their
observation is a challenge for the experiment.
Gas-phase reactions involving
noble-gas ions
The species recalled in the previous paragraphs illustrate
the ability of the noble gases to behave as ligands of ionic
species. In the last decade, mass spectrometric techniques
and theoretical calculations have also been extensively
employed to explore gas-phase reactions involving noblegas ions, especially cations. Surveyed here is, in particular, a group of ionic processes involving singly-charged
xenon cations 219–232 and a series of bond-forming reactions involving doubly-charged cations. 233–247 The implications of these findings for the chemistry of certain xenon
compounds observed in the condensed phases are also
briefly examined.
442
Formation and reactivity of singly-charged
xenon cations
Xenon difluoride (XeF2) is of special interest in xenon chemistry, as it is extensively employed to synthesize a large variety
of xenon compounds.10 The most relevant chemical property
of XeF2 is its Lewis basicity. In particular, when reacted with
strong Lewis acids such as AsF5, SbF5 and BiF5, it behaves
as a fluoride ion donor, forming XeF+ and Xe2F3+, which are,
in turn, precursors of numerous other xenon compounds.10
When reacted with weak or moderate Lewis acids, XeF2 still
behaves as a fluorine base, but without “complete” transfer
of F–. This occurs, for example, with various metal cations
and with neutral molecules such as WOF 4 and MoOF4.10 In
any case, both the salt-like and the fluorine-bridged formulations of these Xe(II) species show that XeF+ is a Lewis acid of
significant strength.10 These considerations stimulate interest
for the gas-phase reactivity of XeF+, which was investigated
in a series of strictly related experimental and theoretical
studies.219–224 The cation was generated from the EI of XeF2248
(at variance with other xenon compounds, xenon difluoride is
quite stable and sublimes easily, even at room temperature,
without decomposition) and produces Xe+, XeF+ and XeF2+. It
is of interest that, at the relatively high pressures typical of
the CI sources, the spectrum of neat XeF2 also includes the
secondary ions Xe2F+, Xe2F2+ and Xe2F3+.219 The reactions of
XeF+ with various nucleophiles (Nu’s) and other related ionic
processes, were subsequently investigated by TQ, FT-ICR and
CI mass spectrometry and the connectivities of the observed
products and reaction intermediates were assayed by MIKE
and CAD spectrometry. The experimental results were invariably supported by ab initio or DFT theoretical calculations. The
observed processes are summarized in Table 9.
In general, the reaction of XeF+ with a given Nu can proceed
by three paths, namely (i) an addition process, followed by
the elimination of a fluorinated molecule (for example, HF),
(ii) a formal transfer of Xe+, with the formation of NuXe+ and
F and (iii) a formal transfer of F+, with the formation of NuF+
and Xe. The only product of the reaction between XeF+ and
HNO3 is XeNO3+.219 The conceivably involved [FXe–O(H)NO2]+
intermediate was not detected in the experiments, but it was
observed219 that the addition of XeF+ to CH3ONO2 produces
a [FXe–O(CH3)NO2]+ adduct, that undergoes the formation of
XeOCH3+ and FNO2 as the only observed unimolecular dissociation. XeNO3+ was also obtained from the reaction between
XeO+ (obtained, in turn, from an ionized mixture of Xe and O3232)
and N2O5 and ascertained to be structurally indistinguishable
from the product of the reaction between XeF+ and HNO3. The
most stable structure of XeNO3+ was, in particular, identified as
the Xe–O–NO2+ isomer. Consistent with this assignment, when
reacted with C2H5NO2, CH3COCH3, CH3CN and C2H5CN under
FT-ICR conditions, XeNO3+ behaved as a nitrating agent.219 The
Xe–O bond distance of Xe–O–NO2+ was theoretically predicted
to be as short as of 2.088 Å and this value is, indeed, quite
close to the X-ray experimental Xe–O distance of 2.126 Å of
the xenon fluoride nitrate FXeONO2, a molecular compound
recently synthesized by reaction of NO2F with [FXeOXeFXeF]
Review of Gas-Phase Chemistry of Noble Gases
[AsF6] at –50°C.249 It is of interest that, in contrast with the
stability of the gaseous XeONO2+, the attempted preparation of
a salt of the XeONO2+ cation by reacting a mixture of FXeONO2
and XeF2 with excess liquid AsF5 at –78 °C revealed the exclusive formation of [XeF][AsF6] and [NO2][AsF6]. These findings
were interpreted249 in terms of the formation of an unstable
[XeONO2][AsF6] salt, that rapidly decomposes into [NO2][AsF6],
Xe and O2. This is a further illustrative case of the actual possibility of employing the isolated conditions of the gas phase
to stabilize noble-gas ionic species, which are short-lived or
even unattainable in the condensed phase. The XeNO2+ cation
was also generated in the gas phase219 by CI ionization of a Xe–
N2O5 mixture and best characterized as a Xe–NO2+ complex,
with a large theoretical Xe–N distance of 3.018 Å.
The reaction between XeF+ and CH3OH220 occurs by a competition between Xe+ and F+ transfer. The CH3O(H)XeF+ intermediate detected from the addition of XeF+ to CH3OH under CI
conditions was characterized as a mixture of the two CH3O(H)–
XeF+ and CH3O(H)–FXe+ isomeric ions, that may evolve into
CH3O(H)Xe+ and CH3O(H)F+ upon loss of F and Xe, respectively.
CH3O(H)F+ was, in particular, identified220 as the O-protonated
isomer of methyl hypofluorite. The observed formation of XeH+
(and presumably CH2O and HF) from the reaction between
XeF+ and CH3OH was also theoretically predicted to be largely
exothermic.
The only product observed from the reaction between XeF+
and C2H4221 was C2H4Xe+, experimentally and theoretically
characterized as a bridged symmetric structure, with two
identical C–Xe distances of 3.207 Å. Strong evidence was also
obtained for the intermediacy in this reaction of a C2H4XeF+
addition product. This ion, not detected from the direct addition of XeF+ to C2H4 was, however, obtained221 from the reaction between Xe2F+ or XeF2+ and C2H4. The CAD spectrum of
C2H4XeF+ showed the XeF+ and C2H4Xe+ fragments and was
suggestive of a Xe–F group linked to C2H4. The calculations
disclosed, in particular, a cyclic complex, in which XeF + is
bound to the p system through the Xe atom. These findings
provided a mechanistic link between the gas-phase results
and the reactions of unsaturated compounds with XeF+ salts,
utilized in solution as stereoselective fluorinating agents.250
As with the reaction with CH3OH, the reactions of XeF+ with
C2H2222 and CH3CN223 produced both the Xe+- and F+-transfer
products. It was shown, in particular, that the addition of XeF+
to these p nucleophiles leads to the Xe-coordinated complexes
[FXe–C 2H 2] + and H 3C–CN–XeF + and to the F-coordinated
complexes [XeF–C2H2]+ and H3C–CN–FXe+ that, in turn, decompose into C2H2Xe+ and H3C–CNXe+ and C2H2F+ and H3C–CNF+,
respectively. The fluorinated products were, in particular,
assigned as H2C=CF+ and H3C–CNF+. The structure of C2H2Xe+
was not explored in further detail, but it is probably analogous
to the bridged symmetric isomer of C2H4Xe+.221 Due to the
similarity of the IE of C2H2, 11.4 eV72 and Xe (see Table 1), the
stability of C2H2Xe+ was attributed to the formation of two resonant structures (C2H2+–Xe and C2H2–Xe+), stabilized by chargeexchange coupling. It is of interest to note here that C2H2Xe+
ions were also so far detected from ionized mixtures of Xe
CI
+
CI
TQ
Cl 2
CH3CN
C 2 H2
®
TQ
+
+
+
TQ
CI
TQ
CI
+
+
+
TQ
CI
TQ
CI
+
FT-ICR
®
®
XeF+ + Cl 2
Cl 2F + Xe
®
XeF + CH3CN
®
®
®
®
®
®
FT-ICR
XeF + CH3CN
XeF + CH3CN
+
XeF + CH3CN
XeF + C2H2
XeF + C2H2
XeF + C2H2
+
®
®
XeF2+ + C2H4
XeF + C2H2
®
Xe2F + C2H4
+
®
XeF+ + C2H4
®
®
XeF + CH3OH
XeF + CH3OH
XeF + CH3OH
®
®
®
TQ
TQ/FT-ICR
+
CI
CH3OH
C2H4
+
XeF + CH3ONO2
CI
CH3ONO2
XeO + N2O5
+
TQ/CI
XeF + HNO 3
+
Conditions
+
HNO 3
Nu
+
XeCl + ClF
+
Cl 2F+ + Xe
H3C-CN-XeF
C2H3NXe + F
+
+
+
H3C-CN-FXe
C2H3NF + Xe
+
[FXe-C2H2]
+
C2H2 Xe + F
+
[XeF-C2H2]
+
C2H2F + Xe
+
[FXe-C2H4] + F
+
[FXe-C2H4] + Xe
+
C2H4 Xe+ + F
XeH + CH2O + HF
+
CH3O(H)-FXe
CH3O(H)-XeF
+
[FXe-O(CH3)NO2]
XeNO 3 + NO 3
+
XeNO 3 + HF
+
Reaction
+
®
®
®
®
®
®
®
®
®
H3C-CNXe + F
+
H3C-CNF + Xe
+
C2H2 Xe + F
+
C2H2F + Xe
+
C2H4 Xe + 2F
+
C2H4 Xe + Xe + F
+
CH3O(H)F + Xe
+
CH3O(H)Xe + F
+
XeOCH3 + FNO2
+
224
224
223
223
223
223
222
222
222
222
221
221
221
220
220
220
219
219
219
Ref.
Table 9. Ionic processes occurring in gaseous mixtures of XeF2 and nucleophilic species (Nu) as observed by TQ, CI, and FT-ICR mass spectrometry. The unimolecular decompositions of the
reaction intermediates (in square brackets) were assayed by CAD or MIKE spectrometry.
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)443
444
and C2H232,34 and subsequently observed by ligand-exchange
between Xe2+ and C2H2.251 As for H3C–CNXe+, its connectivity
was assigned as H3C–C–N–Xe+.223 Other examples of recently
investigated gaseous Xe–N cations will be discussed below.
A formal transfer of F+ was observed from the reaction
between XeF+ and Cl2.224 The Cl2F+ product has an asymmetric
bent structure Cl–Cl–F+ (1A1), that is more stable than the
symmetric Cl–F–Cl+ isomer by more than 167 kJ mol–1. The Cl3+
cation was also investigated and the comparison of the Cl+ and
F+ binding energies to simple halogenated molecules showed
an excellent linear correlation, which was not, however, the
case when the comparison was extended to the PAs. Finally, it
is of interest to note the formation of XeCl+ from the reaction
between Cl2F+ and Xe.224 This cation has, in fact, also been
observed in the solid state as a salt of Sb2F11–.252
The XeF+(Nu) intermediates involved in the above-mentioned
reactions are exemplary cases of adducts of XeF+ with Lewis
bases. Numerous other XeF+(Nu) complexes have also been
obtained by flowing afterglow mass spectrometry.227 These
adducts were formed by termolecular addition of XeF+ to Nu
in the flow reactor, as well as by ligand exchange reactions.
A key species in this regard is the water complex, XeF+(H2O),
attainable from the ionization of XeF2 in the presence of a
small amount of air or water vapor which are able to undergo
ligand exchange with a wide variety of bases, including ethers,
alcohols, carbonyls, aromatic compounds, nitriles and sulfurcontaining molecules. The sampled compounds were nucleophiles stronger than H2O and their PA was invariably higher
than the PA of H2O (691.0 kJ mol–1 72). Bases weaker than water
do not react with XeF +(H2O), but can still form complexes
with XeF+ by termolecular addition. It was thus possible to
observe the adducts of XeF+ with CO, N2O, CH4 and CO2. Even
though the observed XeF+(Nu) were partly characterized by
­structurally-diagnostic mass spectrometric experiments,227
further work is still needed to unravel their detailed structure
and stability.
As mentioned above, under CI conditions, the ionization of
XeF2 produces the secondary ions, Xe2F+, Xe2F2+ and Xe2F3+.219
The latter cation, in particular, has been observed as a salt of
AsF6– since the late 1960s.253 Spectroscopic methods revealed
a F–Xe–F–Xe–F+ connectivity, slightly bent at the central F
atom. Theoretical calculations predict instead a perfectly
linear structure,254,255 and the deviation from linearity in the
crystal is ascribed to the presence of the counterion. It is
of interest that the results of structurally-diagnostic mass
spectrometric experiments revealed225 that, while the fragmentation pattern of the gaseous Xe2F3+ is not inconsistent
with the F–Xe–F–Xe–F+ connectivity, at least a fraction of the
sampled ions is identified as an asymmetric species, structurally assigned as F–Xe–XeF2+.
The H3C–CN–XeF+ adduct observed from the addition of
XeF+ to CH3CN223 is reminiscent of a large group of Xe–N
cations, observed in the solid or liquid phase, that arise from
the interaction of XeF+ with Lewis nitrogen bases such as
hydrogen cyanide, alkylnitriles, pentafluorobenzenenitrile,
perfluoroalkylnitriles, perfluoropyridines and s-trifluoro-
Review of Gas-Phase Chemistry of Noble Gases
triazine.256,257 In these complexes, the xenon–nitrogen interaction is relatively tight and the observed Xe–N distances
range around 2.2–2.3 Å. A second group of condensed-phase
Xe–N cations includes (FO2S)2NXe+,258,259 F5SN(H)Xe+,257,260
F5TeN(H)Xe+,261 and F4S=NXe+.257,262,263 These species can be
regarded as a Xe atom that interacts with the nitrenium ions
(FO2S)2N+, F5SN(H)+, F5TeN(H)+ and F4S=N+ and are invariably
characterized by covalent Xe–N bonds, with short distances
of nearly 2.0–2.1 Å. Very recently,231 the xenon–difluoronitrenium cation F2N–Xe+ was obtained in the gas phase from
Reaction (2)
F2N–FH+ + Xe ® F2N–Xe+ + HF
(2)
observed by IT-MS. Based on theoretical results, the ionic
product was unambiguously assigned as F2N–Xe+. Assuming
the formation of this isomer, Reaction (2) is, in fact, exothermic
by 17.6 kJ mol –1. On the other hand, assuming the formation of the alternative Xe-inserted isomer, F–N–Xe–F+, that
is theoretically predicted to be less stable than F2N–Xe+ by
340.2 kJ mol –1, Reaction (2) results in being prohibitively
endoergic to be observed by IT-MS. According to the theoretical calculations, F2N–Xe+ is a weak electrostatic complex
between NF2+ and Xe, with a Xe–N bond length of 2.4–2.5 Å
and a dissociation enthalpy into its constituting fragments of
63 kJ mol–1. The Xe–N distance of F2N–Xe+ is, however, shorter
than the Xe---N contacts in the “solvated” cations C6F5Xe+--NºCCH3264 and C6F5Xe+---NC5H3F2,265 measured as 2.6–2.7 Å
in solid salts with different anions. Overall, F2N–Xe+ appears
as a peculiar case of borderline species, stable enough to be
detected under the isolated conditions of the gas phase. In this
regard, it is of interest to note that the N2F4 and Xe products
observed so far from the reaction between XeF 2 and HNF2
were ascribed to the formation of F 2NXeF,266 even though
neither this intermediate nor other related ionic species could
be detected, even at lower temperatures.
Equation (2) describes the nucleophilic displacement of HF
from the F-protonated isomer of NF3 by Xe. A process like this
was first reported by Holtz and Beauchamp,267 who observed
Reaction (3)
H3C–FH+ + Xe ® H3C–Xe+ + HF
(3)
Minor Ng–C cations (Ng = Ar, Kr, Xe) had previously
been detected from ionized mixtures of Ng and hydro­
carbons, 32,33,35,268,269 and these studies anticipated the
synthesis of the first Xe–C compounds, obtained in 1989 in
the form of derivatives of the perfluorophenylxenon(II) cation
C 6F 5Xe +. 270–272 Numerous xenon–carbon compounds were
subsequently reported,12,273 and molecules with Kr–C bonds
were recently detected in cold matrices.2,16 Under the isolated
conditions of the gas phase, it was also possible to obtain
cationic species with Ng–Si (Ng = Ar, Kr, Xe),228,229 and Xe–Ge
bonds.230 Their forming reactions are strictly analogous to
those described by Equations (2) and (3). The trifluorosylilxenon cation F3Si–Xe+ was first detected228 from the reaction
between SiF4H+ and Xe, observed by low-pressure FT-ICR
mass spectrometry:
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)445
F3Si–FH+ + Xe ® F3Si–Xe+ + HF
(4)
In a subsequent study performed under the higher pressure
conditions of a SIFT mass spectromer,229 the F3SiXe+ ions were
prepared from the direct addition of SiF3+ to Xe and the Ar and
Kr homologous F3SiAr+ and F3SiKr+ could also be observed.
It is of interest that the multi-CID experiments performed
to probe the connectivities of F3SiXe+ and F3SiKr+ revealed
not only the expected formation of the F3Si–Xe+ and F3Si–Kr+
isomers, but also the remarkable and somewhat surprising
formation of additional isomers, detected at elevated collision energies. Based on the results of theoretical calculations,
these high-energy structures were, in particular, assigned
as the “inserted” isomers F2Si–Ng–F+ and/or F–Ng–F–SiF+
(Ng = Kr, Xe). These ions are less stable than the corresponding
F3Si–Ng+ by hundreds of kilojoules per mol. However, highenergy collisions allow the insertion of Ng atoms into SiF 3+,
with formation of F2Si–Ng–F+ and/or the bond redisposition,
with formation of F–Ng–F–SiF+. Only the low-energy isomer
F3Si–Ar+ was instead detected from the addition of SiF3+ to Ar.
The addition of Xe to CF3+ was also explored,229 but no F3CXe+
was detected. This is consistent with the fact that the Lewis
acidity of CF3+ is considerably lower than SiF3+.274 It is, however,
of interest to note here that, while Si+, SiH+ and SiH2+ are totally
unreactive toward Ar, Kr and Xe,229 XeCF+ and XeCF2+ cations
could be observed by collisions of Xe+ with fluorinated selfassembled monolayer surfaces.275–277
The gas-phase reactions of GeF3+ and GeF 4H +, recently
investigated by IT-MS and theoretical calculations, 230,278
showed numerous similarities with those observed previously for SiF3+ and SiF4H+. In particular, as with SiF4H+, GeF4H+
reacts with Xe230 and undergoes the ligand displacement reaction described by Equation (5):
F3Ge–FH+ + Xe ® F3Ge–Xe+ + HF
(5)
Based on theoretical calculations, the ionic product was
unambiguously assigned as the trifluorogermylxenon cation
F3Ge–Xe+. In fact, this isomer resulted in being more stable than
the Xe-inserted isomer F2Ge–Xe–F+ and the bond-­redisposed
isomer FGe–F–Xe–F + by 392.5 kJ mol –1 and 340.2 kJ mol –1,
respectively. Assuming the formation of F3Ge–Xe+, reaction (5)
is, in particular, predicted to be endothermic and endoergic by
17.6 kJ mol–1 and 15.5 kJ mol–1, respectively, and such a slightly
endoergic processes can actually be observed under IT-MS
conditions. It is of interest that the theoretical calculations
revealed that the Ge–Xe bonding of F3Ge–Xe+ has a somewhat
peculiar mixed ionic–covalent-induction character, where one
picture may overlap with another. The Ge–Xe bond distance,
predicted as 2.615 Å, is only about 0.1 Å longer than the sum of
the single-bond covalent radii279 of Ge, 1.21 Å and Xe, 1.31 Å and
the analysis of the atomic charges indicated a positive charge
of 0.394 e on the Xe atom. This arises from induction effects
by the Ge atom, whose atomic charge reduces from 2.638 e to
2.358 e passing from GeF3+ to F3Ge–Xe+. The fluorine charge of
the F atoms remains, instead, essentially unchanged (–0.546 e
in GeF3+ and –0.584 e in F3Ge–Xe+). In addition, the study of the
topology of the electron density on the Ge–Xe bond of F3Ge–Xe+
furnished values, that are at the overlap between a closedshell (ionic) and a covalent interaction.
Finally, it is of interest to recall here the boron cations F2BNg+
(Ng = Ar, Kr, Xe).226,280 The F2BAr+ was experimentally detected
in the CI spectrum of a BF3/Ar mixture,226 but its structure,
stability and bonding nature were not investigated in further
detail. According to very recent theoretical calculations,280
this cation is assigned as the planar F2B–Ar+ of C2n symmetry,
the only minimum identified on the (F2,B,Ar)+ potential energy
surface. On the other hand, for both (F2,B,Kr)+ and (F2,B,Xe)+,
the calculations disclosed two distinct isomers, namely the
F2B–Kr+ and F2B–Xe+ global minima of C2n symmetry and the
linear F–Kr–B–F+ and F–Xe–B–F+, which are less stable than
the C2n isomers by hundreds of kilojoules per mol. As with the
previously investigated isoelectronic FNgBO281 and FNgBN–,218
the FNgBF+ (Ng = Kr, Xe) are predicted to be metastable highenergy minima, hardly accessible from the addition of Kr or Xe
to BF2+. This process is, instead, at least in principle, a viable
route to the still unobserved F2B–Kr+ and F2B–Xe+. The analysis of the atomic charges and the study of the topology of the
electron density revealed280 that the B–Ng bonds of F2B–Ng+
(Ng = Ar, Kr, Xe) are mostly electrostatic and best described as
ion-induced dipole interaction. The B–Ng bonds of the linear
F–Kr–B–F+ and F–Xe–B–F+ are instead covalent in nature.
In conclusion, under the isolated conditions of the gas phase,
it was possible to observe a variety of xenon cations, including
species that are elusive or unattainable in the condensed
phase. Representative examples among the above-discussed
species are shown in Figure 7.
Bond-forming reactions involving doublycharged cations: moving up the threshold of
reactivity
The reactions between molecular dications (indicated here as
XY2+; X, Y = atom or polyatomic group) and Ng atoms usually
proceed by ET, with formation of XY+ and Ng+, DET, with formation of, for example, X+, Y and Ng+ and CID, with formation
of X+, Y+ and Ng, or, for example, X2+, Y and Ng.97,98 However,
in certain circumstances, it is also possible to observe the
fixation of Ng atoms according to reactions such as those
described by Equations (6)–(8):
XY2+ + Ng ® XYNg2
(6)
XY2+ + Ng ® YNg2+ + X
(7)
XY2+ + Ng ® YNg+ + X+(8)
These processes normally compete with ET or DET and the
model proposed to rationalize this competition97,235,282,283 is
schematized in Figure 8. The left-hand side of the diagram
shows that, in order for the XY2+ and Ng reactants to achieve
the intimate contact they require to form new chemical bonds,
the XY 2+/Ng encounter complex must first overcome the
curve-crossing in the entrance channel that leads to ET and
118
446
Review of Gas-Phase Chemistry of Noble Gases
Figure 7
F
2.066
O
126.3
Xe
1.756
2.088
Xe
1.192
N
O
O
3.207
H
H
C
C
N
1.443 1.141 1.270
H
H
H
C
3.590
F
2.045 (Ar)
2.123 (Kr)
2.280 (Xe)
B
1.254 (Ar)
1.265 (Kr)
1.273 (Xe)
C
H
Xe
N
Xe
Xe
F
1.970
Xe
2.562
2.467 N
104.9
F
H
C 1.390 C
1.444 1.149 2.324
Ar/Kr/Xe
(Ar) 107.9
(Kr) 110.5
(Xe) 112.6
2.777
H
C 1.400 C
Xe
F
Xe
102.3
1.306
F
F
104.5
Si
2.615
F
1.554
101.6
F
F
F
F
Ge
1.669
119
F
Figure 7. Theoretical connectivities and main geometrical parameters (distances in Å and angles in degrees) of xenon cations observed
in the gas phase (data from References 219, 221, 223, 229 to 231 and 280).
Figure 8
XY2+ + Ng
YNg2+ + X
2
1
XY+ + Ng+
YNg+ + X+
[XYNg]2+
Figure 8. Schematic energy diagram showing the occurrence
of bond-forming reactions from XY2+ + Ng. To avoid DET, the
reactants must overcome the crossing point 1 (adapted from
Reference 235).
eventually to DET (point 1). According to the Landau–Zener
theory,97,284,285 the ET occurs when the crossing between the
reactants and products potential energy surfaces fall at internuclear distances between 2 Å and 6 Å (the so-called “reaction window”). Assuming that the XY2+–Ng encounter complex
overcomes point 1, the formed XYNg2+ adduct could be trapped
as it is [Equation (6)], or dissociate into, for example, YNg2+ and
X [Equation (7)]. The latter process essentially describes the
nucleophilic displacement of X by Ng from XY2+. Alternatively,
XYNg2+ could pass through the curve-crossing point 2 and
undergo the formation of, for example, YNg+ and X+ according
to Equation (8).
A first example of fixation of Ng atoms by molecular dications was reported in 1994 by Price et al.,233 who noticed
the minor (less than 1% of the ion yield) but well detected
formation of XeF+ or XeO+ from the reactions of Xe atoms with
CFn2+ (n = 2, 3), SFn2+ (n = 2–4) and CO22+, at laboratory-frame
collision energies between 30 eV and 50 eV. The formation
of ArC2+ from the reaction between CO2+ and Ar was subsequently reported,234 and this reaction was a first example of
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)447
the formation of a chemical bond in a process that involves
doubly-charged cations both as reactants and products. It was,
however, only in the last few years that reactions such as those
described by Equations (6)–(8) have clearly emerged.235–243
For certain observed processes, it was particularly important to sample collision events at very low collision energies.
Theoretical calculations have also been extensively performed
in conjunction with the experiments. A list of observed reactions is given in Table 10.
The hydrogen-containing dications, CHX2+ (X = F, Cl, Br, I),
formed by dissociative EI of the respective methyl halide
precursor molecules, react with Ng atoms (Ng = Ne, Ar, Kr,
Xe)236,237 and undergo the competitive occurrence of PT, with
formation of NgH+ and CX+ and ET, with formation of CHX+
and Ng+. The competition between these two channels was,
in particular, investigated by measuring the branching ratios
between NgH+ and Ng+237 and it was possible to deduce the
following general trends. When the ET between the dication
and the Ng atom is endothermic, or exothermic by less than
2 eV (outside the Landau–Zener reaction window), PT represents the main route of reaction. As soon as the ­exothermicity
of ET exceeds 2 eV, the latter channel predominates and PT
is suppressed, disregarding its actual exothermicity. In practice, with the exception of CHF2+ that is unreactive toward Ne
Table 10. Bond-forming reactions from collisions between molecular dications (obtained from the electron ionization of M) and Ng atoms.
These processes usually compete with ET, DET and CID.
M
CH3Cl
Reaction
2+
CHCl +Ar
2+
Ref.
+
+
®
ArH + CCl
+
236
+
CH3X (X = F, Cl, Br, I)
CHX + Ng (Ng = Ne, Ar, Kr, Xe)
®
NgH + CX
237
CH3Br
[C,H3,Br]2+ + Ng (Ng = Ar, Kr, Xe)
®
NgCH2+ + HBr+
238
[C,H3,Br]2+ + Ng (Ng = Ar, Kr, Xe)
®
NgH+ + CH2Br+
238
C 2 H2
C2H22+ + Ng
C2H22+ + Ng
Toluene (C7H8)
(Ng = Ar, Kr)
(Ng = Ne, Ar, Kr, Xe)
C7H62+ + Xe
®
C7H72+ + Xe
®
C7H82+ + Xe
®
C7H82+ + Xe
®
C9H82+ + Xe
®
C9H62+ + Xe
2,4,6-Trimethylpyridine (C 8H11N)
®
2+
C 8H6N + Xe
2+
C 8H7N + Ng (Ng = Kr, Xe)
2+
C 8H8N + Ng (Ng = Kr, Xe)
2+
C 8H9N + Ng (Ng = Kr, Xe)
C 8H10N2+ + Ng (Ng = Kr, Xe)
3-Vinylpyridine (C7H7N)
2+
C7H7N + Xe
2+
C7H6N + Xe
N,N-Dimethylaniline (C 8H11N)
2+
C 8H9N + Xe
2+
C 8H7N + Xe
CF4
CF 32+ + Ar
CFn2+ + Xe
SiF4
SF6
(n = 2, 3)
(Ng = Ne, Ar)
2+
SF + Ar
2+
CO
CO + Ar
CO2
CO22+ + Xe
®
®
®
(n = 2–4)
HCCNg + H
+
NgH + C2H
C7H6Xe
+
2+
239
239
240
+
XeH + C7H5
+
240
2+
240
2+
240
+ C7H7+
240
C9H8Xe
2+
241
C9H6Xe
2+
C7H7 Xe
C7H6Xe + H2
XeH
+
241
C 8H6NXe
2+
241
2+
241
2+
241
2+
C 8H7NNg
C 8H8NNg
®
C 8H7NNg + H2
241
®
C 8H8NNg2+ + H2
241
®
®
®
®
®
SiF 32+ + Ng
SFn2+ + Xe
®
®
C7H62+ + Xe
Isopropylbenzene (C9H12)
®
2+
®
C7H7NXe
2+
241
C7H6NXe
2+
241
C 8H9NXe
2+
241
C 8H7NXe
2+
241
ArCF2 + F
242
2+
XeF
+
+ CFn–1+
233
2+
243
®
2+
ArS + F
235
®
+
233
®
NgSiF2 + F
XeF
+ SFn–1+
®
2+
ArC + O
234
®
XeO+ + CO +
233
448
and undergoes nearly exclusively ET with Ar, Kr and Xe, PT
predominates in the reactions involving Ne and Ar, while ET
predominates in the reactions involving Kr and Xe. A PT to
the Ng atom was also observed from the reaction between
[C,H3,Br]2+ (assumed to be a mixture of the tautomeric ions
CH2BrH2+ and CH3Br2+) and Ar, Kr and Xe.238 By far the most
noticeable products detected from these reactions were,
however, the noble-gas carbene cations, NgCH2+ (Ng = Ar, Kr,
Xe), and the formation of ArCH2+ was, in particular, investigated by DFT calculations.238 This product was found to arise
from the singlet ground state ylide, CH2BrH2+ (the most stable
[C,H3,Br]2+ isomer), in an overall exothermic process. The
mechanism involves a Ar–CH2BrH2+ encounter complex, with
argon coordinated to carbon, from which the loss of HBr +
concomitant with charge separation leads to ArCH2+ with an
overall exothermicity of 210.3 kJ mol–1. The energy released
is significantly larger than the energy of the Ar–C bond in the
product, D(Ar–CH2+) = 81.0 kJ mol–1. Accordingly, the consecutive fragmentation into Ar + CH2+ is energetically feasible and
it is most probably responsible for the low yield of the bondforming product ArCH2+.
Bond-forming reactions were also observed from collisions with Ng atoms of dications obtained from the EI of
unsaturated and aromatic molecules. 239–241 The C 2 H 2 2+
produced from acetylene react with all the noble gases with
the exception of He and undergo PT, ET and DET. 239 The
most noticeable observation was, however, the formation
of HCCAr2+ and HCCKr2+ from the reactions with Ar and Kr.
It is of interest that these experimental findings confirmed
previous theoretical predictions about the stabilities
of noble-gas acetylides. 286 In particular, the formation of
HCCAr2+ from C2H22+ and Ar was investigated in detail. The
experiments revealed that this process is endothermic and,
based on measurements of the reactivity of the monodeuterated dication C2HD2+, it was possible to derive a kinetic
isotope effect of 1.7 ± 0.1 in favor of losing an H rather than a
D moiety from the acetylenic species, i.e. DCCAr2+ is formed
preferentially. This was attributed to the larger number of
accessible vibrational states at the transition state upon
cleaving a C–H bond. Based on exploratory DFT calculations, the formation of HCCAr2+ from the triplet ground state,
C2H22+, was predicted to be endothermic and involving the
intermediacy of a Ar–C2H22+ encounter complex, with argon
coordinated to carbon which, in turn, undergoes the direct
elimination of a H atom. It was also observed that the reactions of mass-selected C2H22+ with He, Ne and Xe yield no
C–Ng bond-forming products. These trends of reactivity of
the Ng atoms with C2H22+ were rationalized by comparing
the energetics of the ET and PT reactions with those of the
bond-forming channels. The calculations revealed, in particular,239 that the formation of HCCNg 2+ from the acetylene
dication is endothermic with Ng = He, Ne, Ar and Kr and only
weakly exothermic with Xe. However, for Kr and Xe, ET and PT
are also largely exothermic and compete efficiently with the
formation of the first encounter complexes, HCCHKr 2+ and
HCCHXe2+. Consequently, only a minor HCCKr2+ is detected
Review of Gas-Phase Chemistry of Noble Gases
from the reaction between HCCH2+ and Kr and no HCCXe2+ is
observed from the reaction between HCCH2+ and Xe.
Organoxenon dications were observed from collisions with
xenon of the C7Hn2+ dications (n = 6–8) generated by double
ionization of toluene.240 No other noble gas was found to react
with these ions and no bond-forming reactions were observed
with hydrogen-depleted dications (n ≤ 5). Both C7H62+ and
C7H72+ react with xenon and form the corresponding C7H6Xe2+
and C7H7Xe2+ complexes by termolecular collisional stabilization. These processes are, indeed, exemplary cases of reactions such as those described by Equation (6). The formation
of C7H7Xe2+ is, however, only observed at elevated xenon pressures and is much less efficient than the formation of C7H6Xe2+.
Retarding-potential analysis, reactive monitoring with
synchrotron radiation and DFT calculations also consistently
revealed that the formation of C7H6Xe2+ and H2 from C7H82+
and Xe occurs as a slightly endothermic, direct ­substitution
of dihydrogen by the rare gas with an expansion to a sevenmembered ring structure as the key step. The predicted
most stable isomer of C7H6Xe2+ is an adduct between the
cycloheptatrienyldiene dication and xenon, whose computed
binding energy of 131.2 kJ mol–1 reaches the strength of a
weak covalent bond. The formation of organoxenon dications
is not, however, a general feature of the dications generated
by double ionization of hydrocarbons. Thus, among the various
CmHn2+ generated from benzene, cyclooctatetraene, m-xylol,
ethylbenzene, propylbenzene, isopropylbenzene, mesitylene,
4-ethyltoluene and butylbenzene,241 only the C9H82+ and C9H62+
from isopropylbenzene react with xenon, leading to C9H8Xe2+
and C9H6Xe2+, respectively. Two dications from 4-ethyltoluene,
namely C9H92+ and C9H62+, also slightly react with xenon, but
the relative intensities of the resulting organoxenon dications
are less than 1%. On the other hand, it was observed241 that
the C8HnN2+ (n = 6–10) obtained from the EI of 2,4,6-trimethyl­
pyridine react with xenon to form C8H6NXe2+, C8H7NXe2+ and
C8H8NXe2+. Strictly analogous products were also detected
from the reactions of the same C8HnN2+ dications (n = 7–10)
with krypton. The fixation of xenon was also observed from
the collisions of Xe atoms with dications obtained from ionized
N,N-dimethylaniline and 3-vinylpyridine. 241 Other mediumsized N-containing dications generated by dissociative EI of a
series of nitrogen heterocycles, anilines and also benzonitrile
revealed, however, to be unable to undergo such bond-forming
reactions.
Remarkable bond-forming reactions were also observed
from the collisions of Ng atoms, particularly Ar, of the doublycharged fluorinated cations CF 32+,242 SiF32+,243 and SF2+.235
The reactions of both CF32+ and SiF32+ with noble gas atoms
had been the subject of previous investigations conducted at
elevated collision energies.287–289 However, under these experimental conditions, the only observed processes were ET and
neutral loss. On the other hand, working at q
­ uasi-thermal
collision energies, CF32+ reacts with argon,242 and forms
ArCF22+, a further example of molecular species with a C–
Ar bond. The overall reaction is theoretically predicted to be
exothermic by 132.2 kJ mol–1 and the product is characte-
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)449
rized as a bound species, with an Ar–C bond only slightly
longer than a typical Ar–C s bond. Under the same experimental conditions, except for a very weak signal which might
correspond to KrCF22+, none of the other noble gases undergo
bond-forming reactions with CF32+. These observations were
rationalized242 by the operation of two distinct effects. For the
heavier Kr and Xe, ET leading to charge separation reactions is
more and more favored due to the lower IE of these atoms. The
two lighter He and Ne are, instead, resistant to one-electron
oxidation by CF22+, but do not have potential for formation of
strong donor-acceptor complexes with CF22+. As with CF32+, at
low collision energies, SiF32+ reacts with Ar and forms ArSiF22+
as the major observed product channel.243 The overall process
is theoretically predicted to be exothermic by 78.2 kJ mol–1
and the structure and stability of ArSiF22+ point to a covalent
Ar–Si bond. Together with the F3Si–Ar+ cation discussed in
the previous paragraph,229 ArSiF22+ is a further example of a
chemical species with an argon–silicon bond. Quite interestingly, small signals for the isotopes 20NeSiF22+ and 22NeSiF22+
were also observed from the collisions of SiF32+ with Ne.243 The
NeSiF22+ is not only a first example of a neon–silicon compound,
but also a rare example of observed molecular species containing neon. The calculations predicted that the formation of
NeSiF22+ from the ground states of SiF32+ and Ne is endothermic
by 112.9 kJ mol–1. Therefore, it was concluded243 that NeSiF22+
is, most probably, formed from one of the excited states of the
SiF32+ precursor dication that are accessible from the electron
ionization of SiF4.290 Finally, the ArS2+ observed from the collisions between SF2+ and Ar235 is a rare example of a molecular
species with an Ar–S bond. According to theoretical calculations, the lowest-lying singlet and triplet states of ArS2+ are
bound and are both energetically accessible at the collision
energies sampled in the experiments (between 6 eV and 14 eV
in the laboratory frame).
Argon cations were also observed from the reactions
between Ar2+ and N2,244 CO and CO2,245 O2246 and NH3.247 The
reaction with N2244 leads to ArN2+ according to Equation (9):
Ar2+ + N2 ® ArN2+ + N
(9)
This process was a first reported example of production
of noble-gas dications by bimolecular reactions. Its cross
section was measured at relative collision energies from
thermal to 20 eV (centre-of-mass reference frame) and the
obtained results indicated the operation of probably different
reaction mechanisms. In addition, the observation of products
at collision energies lower than the reaction endothermicity
(estimated as 129.3 kJ mol–1) suggested the possible presence
of metastable Ar2+ (1D or 1S), which are likely to be responsible
for the formation of excited products. The mechanism of the
observed reaction(s) was, however, not explored in further
detail. It is of interest that the reaction between Ar2+ and
N2 is the doubly-charged counterpart of the experimentally
observed endothermic formation of ArN+ from the reaction
between Ar+ and N2.291 Estimates of the reaction thresholds of
this process and symmetry considerations suggested that the
ArN+ product ion is in its first excited state, A 3P. It is of interest
that the ArN+ obtained from the symmetric reaction between
N2+ and Ar was identified as the ground state, X 3S.291
The diatomic ArC2+ is obtained from the reaction of Ar2+ with
both CO and CO2245 according to Equations (10) and (11):
Ar2+ + CO ® ArC2+ + O
(10)
Ar2+ + CO2 ® ArC2+ + 2O
(11)
In spite of the metastability of ArC2+ predicted by theory,292,293
previous attempts to observe ArC2+ by charge stripping of ArC+
had not been successful.294 The study of the cross section of
Reaction (10) as a function of the collision energy revealed the
occurrence of an exothermic reaction, that is likely to occur on
the 3S ground-state surface. As for Reaction (11), the experiments point, instead, to an endothermic process and this rules
out the conceivable alternative formation of O2 as a reaction
product. In any case, due to the most prevailing occurrence of
ET processes, the cross sections of both Reactions (10) and
(11) are quite small (< 0.1 Å2) compared to the values typical of
ion–molecule reactions.
When reacted with O2,246 Ar2+ forms ArO2+ and ArO+ according to Equations (12) and (13):
Ar2+ + O2 ® ArO2+ + O
(12)
Ar2+ + O2 ® ArO+ + O+(13)
As with Reactions (10) and (11), the cross sections of these
processes are, in general, much smaller than those of the
competitive ET processes producing O+ and O2+. A plot of the
cross section of Reaction (12) as a function of the collision
energy suggested that this process could be either exothermic
or slightly endothermic. To work out this problem, accurate
ab initio calculations were performed to investigate the lowlying electronic states of ArO2+.246 Assuming the formation
of the ground-state, 3S–, Reaction (12) was predicted to be
exothermic by 277.9 kJ mol–1. However, the estimated lifetime
of this metastable state of ArO2+ was too short to support its
conceivable detection by the employed experimental set-up.
It was therefore concluded that the observed ArO2+ were the
higher-lying states, 1D and/or 1S+. Assuming the formation
of these states, Reaction (12) resulted in being exothermic
by 126.4 kJ mol–1 and 46.3 kJ mol–1, respectively. Concerning
the strongly exothermic Reaction (13), although it was ascertained to proceed at the lowest energies accessible in the
experiments, an apparent threshold was observed at about
1 eV (centre-of-mass reference frame). Above this value, the
cross section increased to reach a broad maximum at about
3 eV. This threshold was tentatively ascribed to the presence
of an exit-channel barrier, due to the coulombic repulsion
between the monocharged species. For some excited states of
ArO+ + O+, this barrier may be higher in energy than the reactants and, therefore, by increasing the collision energy, these
excited products can become accessible and, consequently,
the cross section increase.
Crossed-beam collision experiments revealed247 that Ar2+
and NH 3 form ArNH + and ArN +. The product ion intensity
450
I[ArNH+] decreased by increasing the collision energy, with
a corresponding increase in the I[ArN+] product ion intensity, indicating that ArN+ is formed by dissociation of ArNH+.
This sequential mechanism suggested by the experiments
was confirmed by accurate ab initio calculations performed
to investigate the relevant features of the potential energy
surface of the reaction. The calculations disclosed, in particular, a mechanism in which, starting from the electronically
excited singlet Ar2+ (1D), an ArNH32+ complex is formed, with
a large exothermicity of nearly 1544 kJ mol–1. This complexation is followed by proton loss via a transition state and then
loss of the two remaining hydrogen atoms in two subsequent
activationless steps to give the products 3ArN+ + H+ + 2H. The
calculations also indicated that no bond-forming pathway
exists starting from the triplet ground state Ar2+ (3P). Overall,
even though the most prevailing products from the reaction
between Ar2+ and NH3 were Ar+ and NHx+ (x = 0–3), the formation of ArNH+ and ArN+ is, in any case, remarkable, especially
if one notes that the analogous reaction between Xe2+ and
NH 3, recently investigated by guided-ion beam spectrometry,295 leads exclusively to the ET and DET products NH x+
(x = 1–3).
Concluding remarks
The gas-phase ion chemistry of the noble gases has recently
being enriched with novel species and bonding motifs.
Various research themes are, in particular, expected to
attract further interest in the future. The ionic complexes
ensuing from helium droplets doped with atoms and molecules are fascinating objects that certainly deserve further
investigation. While considerable progress has been made
in the description of helium clustering around monoatomic
ions, further theoretical work is still needed to describe
systems comprising larger molecular ions. The observation of helium attachment to the anionic clusters of simple
amino acids stimulates, in particular, interesting questions
as to the still little explored interaction of noble gas atoms
with ions of biological interest. Valuable information in this
regard is, in particular, expected from infrared photodissociation spectroscopy, successfully employed in recent years
to explore the structure and stability of noble gas complexes
with organic ions. These studies, and other recent applications of the “noble-gas tagging” technique, have also definitely demonstrated that the solvating noble gas atoms are
not simple “messengers” of the spectroscopic properties of
the ionic chromophore. Rather, they interact with the ionic
species and, in principle, appreciably modify not only its
intrinsic absorptions but also its detailed structure. Due to
the widespread interest for the noble-gas tagging technique,
it is expected that these issues will be further investigated by
experiments and theory. Experimental work is also necessary to expand our current knowledge about the existence in
the gas phase of covalent anions of the noble gases, including
the lightest helium, neon and argon. Future searches in this
Review of Gas-Phase Chemistry of Noble Gases
direction could also be guided by recent theoretical predictions of a large family of such species.
Turning to gas-phase reactions involving noble gas ions,
the most noticeable recent advance is certainly the observation of bond-forming reactions from the collisions between
doubly-charged cations and noble gas atoms, including the
lightest argon and neon. As well as allowing the formation of
otherwise elusive noble gas ions, these reactions highlight the
crucial role of collision energies to observe these somewhat
surprising reactive events. Certain processes could, in fact,
only be observed at the lowest collision energies while, at the
higher collisions energies, the noble gas atoms behave as
typical non-reactive targets. It will certainly be of interest to
investigate this fascinating class of reactions in further detail.
Novel evidence has also recently been obtained on gas-phase
ion–molecule reactions involving singly-charged xenon cations.
These studies are also of interest to appreciate the effects of
solvent, counterions and other environmental factors on the
structure, stability and reactivity of xenon cations observed
in the liquid or solid-phase. Despite the variety of already
observed species and reactions, the gas-phase ion chemistry
of xenon compounds still remains little explored and, essentially, no information is available to date on the ion chemistry
of krypton compounds. Bridging these gaps is a challenge for
future experimental and theoretical work.
Acknowledgments
The author wishes to thank all the colleagues who kindly
provided reprints or preprints of their research articles. This
work was financially supported by the Università della Tuscia
and by the Italian Ministero dell’Istruzione, dell’Università
e della Ricerca (MIUR) through the “Cofinanziamento di
Programmi di Ricerca di Rilevante Interesse Nazionale”.
References
1.
2.
3.
4.
5.
G.J. Schrobilgen and D.S. Brock, “Noble gases”, Annu.
Rep. Prog. Chem., Sect. A: Inorg. Chem. 107, 135–141
(2011). doi: 10.1039/C1IC90019F
W. Grochala, L. Khriachtchev and M. Räsänen, “Noblegas chemistry”, in Physics and Chemistry at Low
Temperatures, Ed by L. Khriachtchev. CRC Press, Boca
Raton, Florida, USA, pp. 419–446 (2011).
L. Khriachtchev, M. Pettersson, N. Runeberg, J. Lundell
and M. Räsänen, “A stable argon compound”, Nature
406, 874–876 (2000). doi:10.1038/35022551
S. Seidel and K. Seppelt, “Xenon as a complex ligand:
the tetra xenono gold(II) cation in AuXe42+(Sb2F11–)2”,
Science 290, 117–118 (2000). doi: 10.1126/science.290.5489.117
N. Maggiarosa, D. Naumann and W. Tyrra,
“Bis(pentafluorophenyl)xenon, Xe(C6F 5)2: a
homoleptic diorganoxenon derivative“, Angew.
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)451
Chem. Int. Ed. 39, 4588–4591 (2000). doi:
10.1002/1521-3773(20001215)39:24<4588::AIDANIE4588>3.0.CO;2-5
6. H.-J. Frohn, N. Leblond, K. Lutar and B. Žemva, “The
first organoxenon(IV) compound: pentafluorophenyld
ifluoroxenonium(IV) tetrafluoroborate“, Angew. Chem.
Int. Ed. 39, 391–393 (2000). doi: 10.1002/(SICI)15213773(20000117)39:2<391::AID-ANIE391>3.0.CO;2-U
7. H.-J. Frohn, T. Schroer and G. Henkel, “C6F 5 XeCl and
[(C6F 5 Xe)2Cl][AsF6]: the first isolated and unambiguously characterized xenon(II) chlorine compounds”,
Angew. Chem. Int. Ed. 38, 2554–2555 (1999). doi:
10.1002/(SICI)1521-3773(19990903)38:17<2554::AIDANIE2554>3.0.CO;2-1
8. M. Gerken and G.J. Schrobilgen, “The impact of multiNMR spectroscopy on the development of noble-gas
chemistry”, Coord. Chem. Rev. 197, 335–395 (2000). doi:
10.1016/S0010-8545(99)00188-5
9. K.O. Christe, “A renaissance in noble gas chemistry”, Angew. Chem. Int. Ed. 40, 1419–1421 (2001).
doi: 10.1002/1521-3773(20010417)40:8<1419::AIDANIE1419>3.0.CO;2-J
10. M. Tramšek and B. Žemva, “Synthesis, properties and
chemistry of xenon(II) fluoride”, Acta Chim. Slov. 53,
105–116 (2006).
11. G. Tavćar and B. Žemva, “XeF4 as a ligand for a metal
ion”, Angew. Chem. Int. Ed. 48, 1432–1434 (2009). doi:
10.1002/anie.200803365
12. W. Grochala, “Atypical compounds of gases, which have
been called ‘noble’”, Chem. Soc. Rev. 36, 1632–1655
(2007). doi: 10.1039/b702109g
13. D.S. Brock, J.J. Casalis de Pury, H.P.A. Mercier, G.J.
Schrobilgen and B. Silvi, “A rare example of a krypton
difluoride coordination compound: [BrOF2][AsF6]∙2KrF2”,
J. Am. Chem. Soc. 132, 3533–3542 (2010). doi: 10.1021/
ja9098559
14. D.S. Brock, H.P.A. Mercier and G.J. Schrobilgen, “XeOF 3-,
an example of an AX3YE2 valence shell electron pair
repulsion arrangement; syntheses and structural characterizations of [M][XeOF3] (M = Cs, N(CH3)4)”, J. Am. Chem.
Soc. 132, 10935–10943 (2010). doi: 10.1021/ja103730c
15. R.B. Gerber, “Formation of novel rare-gas ­molecules
in low-temperature matrices”, Annu. Rev. Phys.
Chem. 55, 55–78 (2004). doi: 10.1146/annurev.physchem.55.091602.094420
16. L. Khriachtchev, M. Räsänen and R.B. Gerber, “Noblegas hydrides: new chemistry at low temperatures”, Acc.
Chem. Res. 42, 183–191 (2009). doi: 10.1021/ar800110q
17. J. Li, B.E. Bursten, B. Liang and L. Andrews, “Noble
gas-actinide compounds: complexation of the CUO
molecule by Ar, Kr and Xe atoms in noble gas matrices”, Science 295, 2242–2245 (2002). doi: 10.1126/science.1069342
18. I. Infante, L. Andrews, X. Wang and L. Gagliardi, “Noble
gas matrices may change the electronic structure of
trapped molecules: the UO2(Ng)4 [Ng = Ne, Ar] case”,
Chem. Eur. J. 16, 12804–12807 (2010). doi: 10.1002/
chem.201002549
19. C.J. Evans, T.G. Wright and A.M. Gardner, “Geometries
and bond energies of the He-MX, Ne-MX and Ar-MX
(M = Cu, Ag, Au; X = F. Cl) complexes”, J. Phys. Chem. A
114, 4446–4454 (2010) and references therein. doi:
10.1021/jp912027y
20. N. Bartlett, “Xenon exafluoroplatinate(V) Xe +[PtF6] –“,
Proc. Chem. Soc. 218 (1962). doi: 10.1039/PS9620000197
21. L. Graham, O. Graudejus, N.K. Jha and N. Bartlett,
“Concerning the nature of XePtF6“, Coord. Chem.
Rev. 197, 321–334 (2000). doi: 10.1016/S00108545(99)00190-3
22. I. Hargittai, “Neil Bartlett and the first noble-gas compound”, Struct. Chem. 20, 953–959 (2009). doi: 10.1007/
s11224-009-9526-9
23. T.R. Hogness and E.G. Lunn, “The ionization of hydrogen by electron impact as interpreted by positive ray
analysis”, Phys. Rev. 26, 44–55 (1925). doi: 10.1103/
PhysRev.26.44
24. S.C. Lind and D.C. Bardwell, “A new type of gaseous
catalysis”, Science 62, 593–594 (1925). doi: 10.1126/science.62.1617.593
25. S.C. Lind and D.C. Bardwell, “The ions of inert gases as
catalysts”, Science 63, 310–311 (1926). doi: 10.1126/science.63.1629.310
26. C.E. Melton and P.S. Rudolph, “Transient species in the
radiolytic polymerization of cyanogen”, J. Chem. Phys.
33, 1594–1595 (1960). doi: 10.1063/1.1731463
27. L. Pauling, “The normal state of the helium molecule–
ions He2+ and He2++”, J. Chem. Phys. 1, 56–59 (1933). doi:
10.1063/1.1749219
28. O. Tüxen, “Massenspektrographische untersuchungen negativer ionen in gasentladungen bei höheren
drucken”, Z. Physik A 103, 463–484 (1936). doi: 10.1007/
BF01333171
29. M. Guilhaus, A.G. Brenton, J.H. Beynon, M. Rabrenović
and P.v.R. Schleyer, “He2 2+, the experimental detection of a remarkable molecule“, J. Chem. Soc., Chem.
Commun. 210–211 (1985). doi: 10.1039/C39850000210
30. J.A. Hornbeck and J.P. Molnar, “Mass spectrometric
studies of molecular ions in the noble gases”, Phys. Rev.
84, 621–625 (1951). doi: 10.1103/PhysRev.84.621
31. M.S.B. Munson, J.L. Franhlin and F.H. Field, “A mass
spectrometric study of homonuclear and heteronuclear
rare gas molecule ions”, J. Phys. Chem. 67, 1542–1548
(1963). doi: 10.1021/j100801a034
32. F.H. Field and J.L. Franklin, “Reactions of gaseous
ions. X. Ionic reactions in xenon-methane mixtures”,
J. Am. Chem. Soc. 83, 4509–4515 (1961). doi: 10.1021/
ja01483a004
33. F.H. Field, H.N. Head and J.L. Franklin, “Reactions of
gaseous ions. XI. Ionic reactions in krypton-methane
and argon-methane mixtures”, J. Am. Chem. Soc. 84,
1118–1122 (1962). doi: 10.1021/ja00866a011
452
Review of Gas-Phase Chemistry of Noble Gases
34. P.S. Rudolph, S.C. Lind and C.E. Melton, “Ionic com-
47. M. Theisen, F. Lackner and W.E. Ernst, “Forming Rb +
plexes of Xe and C2H2 produced by the radiolysis of
these gases”, J. Chem. Phys. 36, 1031–1035 (1962). doi:
10.1063/1.1732627
35. L.P. Theard and W.H. Hamill, “The energy dependence
of cross sections of some ion-molecule reactions”,
J. Am. Chem. Soc. 84, 1134–1139 (1962). doi: 10.1021/
ja00866a015
36. M.S.B. Munson, F.H. Field and J.L. Franklin, “Highpressure mass spectrometric study of reactions of rare
gases with N2 and CO”, J. Chem. Phys. 37, 1790–1799
(1962). doi: 10.1063/1.1733370
37. T.A. Carlson and R.M. White, “Decomposition
of (CH3Xe131)+ following the nuclear decay of
CH3I131”, J. Chem. Phys. 36, 2883–2887 (1962). doi:
10.1063/1.1732395
38. T.A. Carlson and R.M. White, “Mass spectrometric
analyses of the ions resulting from the nuclear decay
of CH3I130 and C2H5I131. Study of xenon-hydrocarbon
ions. II”, J. Chem. Phys. 38, 2075–2081 (1963). doi:
10.1063/1.1733935
39. T.A. Carlson and M. White, “Fragmentation of the
excited parent ions, [CH 3Kr 82] + and [CH 3 O18]-, following the b - decay of CH 3Br 82 and the b + decay of
CH 3F18”, J. Chem. Phys. 39, 1748–1752 (1963). doi:
10.1063/1.1734524
40. T. Drews, S. Seidel and K. Seppelt, “Gold-xenon complexes“, Angew. Chem. Int. Ed. 41, 454–456 (2002).
doi: 10.1002/1521-3773(20020201)41:3<454::AIDANIE454>3.0.CO;2-7
41. I.-C. Hwang, S. Seidel and K. Seppelt, “Gold(I) and
mercury(I) xenon complexes”, Angew. Chem. Int. Ed. 42,
4392–4395 (2003). doi: 10.1002/anie.200351208
42. K. Seppelt, “Metal-xenon complexes”, Z. Anorg.
Allg. Chem. 629, 2427–2430 (2003). doi: 10.1002/
zaac.200300226
43. J. Tiggesbäumker and F. Stienkemeier, “Formation and
properties of metal clusters isolated in helium droplets”, Phys. Chem. Chem. Phys. 9, 4748-4770 (2007). doi:
10.1039/B703575F
44. T. Döppner, T. Diederich, S. Göde, A. Przystawik, J.
Tiggesbäumker and K.-H. Meiwes-Broer, “Ion induced
snowballs as a diagnostic tool to investigate the caging of metal clusters in large helium droplets”, J.
Chem. Phys. 126, 244513/1- 244513/7 (2007). doi:
10.1063/1.2745294
45. T. Döppner, Th. Diederich, A. Przystawik, N.X. Truong,
Th. Fennel, J. Tiggesbäumker and K.-H. MeiwesBroer, “Charging of metal clusters in helium droplets
exposed to intense femtosecond laser pulses”, Phys.
Chem. Chem. Phys. 9, 4639–4652 (2007). doi: 10.1039/
B703707D
46. S. Müller, M. Mudrich and F. Stienkemeier, “Alkalihelium snowball complexes formed on helium nanodroplets”, J. Chem. Phys. 131, 044319/1-044319/7 (2009).
doi: 10.1063/1.3180819
snowballs in the center of He nanodroplets”, Phys.
Chem. Chem. Phys. 12, 14861–14863 (2010). doi: 10.1039/
C0CP01283A
48. S. Paolini, F. Ancilotto and F. Toigo, “Ground-state
path integral Monte Carlo simulations of positive ions in 4 He clusters: bubbles or snowballs?”,
J. Chem. Phys. 126, 124317/1–124317/8 (2007). doi:
10.1063/1.2711813
49. E. Coccia, E. Bodo, F. Marinetti, F. A. Gianturco, E.
Yildrim, M. Yurtsever and E. Yurtsever, “Bosonic helium
droplets with cationic impurities: onset of electrostriction and snowball effects from quantum calculations”,
J. Chem. Phys. 126, 124319/1–124319/8 (2007). doi:
10.1063/1.2712437
50. F. Marinetti, Ll. Uranga Piña, E. Coccia, D. LópezDurán, E. Bodo and F.A. Gianturco, “Microsolvation
of cationic dimers in 4 He droplets: geometries of
A 2+ (He) N (A = Li, Na, K) from optimized geometries”, J.
Phys. Chem. A 111, 12289–12294 (2007). doi: 10.1021/
jp0748361
51. A. Hermann, M. Lein and P. Schwerdtfeger, “The search
for the species with the highest coordination number”,
Angew. Chem. Int. Ed. 46, 2444–2447 (2007). doi: 10.1002/
anie.200604148
52. P. Slavíček and M. Lewerenz, “Snowballs, quantum solvation and coordination: lead ions inside small helium
droplets”, Phys. Chem. Chem. Phys. 12, 1152–1161 (2010).
doi: 10.1039/B918186E
53. D.E. Galli, D.M. Ceperley and L. Reatto, “Path integral
Monte Carlo study of 4He clusters doped with alkali
and alkali-earth ions”, J. Phys. Chem. A 115, 7300–7309
(2011). doi: 10.1021/jp200617a
54. J.P. Toennies and A.F. Vilesov, “Superfluid helium droplets: a uniquely cold nanomatrix for molecules and
molecular complexes”, Angew. Chem. Int. Ed. 43, 2622–
2648 (2004). doi: 10.1002/anie.200300611
55. M. Barranco, R. Guardiola, S. Hernandez, R. Mayol, J.
Navarro and M. Pi, “Helium nanodroplets: an overview”,
J. Low Temp. Phys. 142, 1–81 (2006). doi: 10.1007/s10909005-9267-0
56. R.D. Lide (Ed), CRC Handbook of Chemistry and Physics,
73rd Edn. CRC Press, Boca Raton, Florida, USA (1992).
57. D. Bellert and W.H. Breckenridge, “Bonding in groundstate and excited-state A+·Rg van der Waals ions
(A = Atom, Rg = Rare gas atom): a model–potential analysis”, Chem. Rev. 102, 1595–1622 (2002). doi: 10.1021/
cr980090e
58. P. Soldán, E.F.P. Lee, J. Lozeille, J.M. Murrell and T.J.
Wright, “High-quality interaction potential for Li+∙He“,
Chem. Phys. Lett. 343, 429–436 (2001). doi: 10.1016/
S0009-2614(01)00717-5
59. J. Lozeille, E. Winata, L.A. Viehland, P. Soldan, E.P.F.
Lee and T.G. Wright, “Spectroscopy of Li+∙Rg and Li+ -Rg
transport coefficients (Rg = He-Rn)”, Phys. Chem. Chem.
Phys. 4, 3601–3610 (2002). doi: 10.1039/B111675D
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)453
60. L.A. Viehland, J. Lozeille, P. Soldán, E.P.F. Lee and
T.G. Wright, “Spectroscopy of Na+∙Rg and transport
c­oefficients of Na+ in Rg (Rg = He-Rn)” J. Chem. Phys. 119,
3729–3736 (2003). doi: 10.1063/1.1591171
61. L.A. Viehland, J. Lozeille, P. Soldán, E.P.F.Lee and T.G.
Wright, “Spectroscopy of K+∙Rg and transport coefficients of K+ in Rg (Rg = He-Rn)”, J. Chem. Phys. 121,
341–351 (2004). doi: 10.1063/1.1735560
62. H.L. Hickling, L.A. Viehland, D.T. Shepherd, P. Soldán,
E.P.F. Lee and T.G. Wright, “Spectroscopy of M+∙Rg
and transport coefficients of M+ in Rg (M = Rb-Fr;
Rg = He-Rn)”, Phys. Chem. Chem. Phys. 6, 4233–4239
(2004). doi: 10.1039/B405221H
63. W.H. Breckerindge, V.L. Ayles and T.G. Wright,
“Analysis of the bonding in alkali-cation/Rg complexes (Rg = He-Xe) using a simple model potential”,
Chem. Phys. 333, 77–84 (2007). doi: 10.1016/j.chemphys.2007.01.008
64. A.M. Gardner, C.D. Withers, J.B. Graneek, T.G. Wright,
L.A. Viehland and W.H. Breckenridge, “Theoretical
study of M+ –RG and M2+ –RG complexes and transport
of M+ through RG (M = Be and Mg, RG = He-Rn)”, J. Phys.
Chem. A 114, 7631–7641 (2010). doi: 10.1021/jp103836t
65. A.M. Gardner, C.D. Withers, T.G. Wright, K.I. Kaplan,
C.Y.N. Chapman, L.A. Viehland, E.P.F. Lee and W.H.
Breckenridge, “Theoretical study of the bonding in
M n+ -RG complexes and the transport of M n+ through
rare gas (M = Ca, Sr and Ra; n = 1 and 2; and RG = He–
Rn)”, J. Chem. Phys. 132, 054302/1–054302/11 (2010).
doi: 10.1063/1.3297891
66. M.F. McGuirk, L.A. Viehland, E.P.F. Lee, W.H.
Breckenridge, C.D. Withers, A.M. Gardner, R.J.
Plowright and T.G. Wright, “Theoretical study of
Ba n+ -RG (RG = rare gas) complexes and transport of
Ba n+ through RG (n = 1, 2; RG = He-Rn)”, J. Chem. Phys.
130, 194305/1–194305/9 (2009). doi: 10.1063/1.3132543
67. A.M. Gardner, K.A. Gutsmiedl, T.G. Wright, W.H.
Breckenridge, C.Y.N. Chapman and L.A. Viehland,
“Theoretical study of Al+ -RG (RG = He-Rn)”, J.
Chem. Phys. 133, 164302/1–164302/6 (2010). doi:
10.1063/1.3494602
68. A.M. Gardner, K.A. Gutsmiedl, T.G. Wright, E.P.F. Lee,
W.H. Breckenridge, S. Rajbhandari, C.Y.N. Chapman
and L.A. Viehland, “Theoretical study of M+ -RG complexes (M = Ga, In; Rg = He-Rn)”, J. Phys. Chem. A 115,
6979–6985 (2011). doi: 10.1021/jp1122079
69. B.R. Gray, E.P.F. Lee, A. Yousef, S. Srestha, L.A.
Viehland and T.G. Wright, “Accurate potential energy
curves for Tl+ -Rg (Rg=He–Rn): spectroscopy and transport coefficients”, Mol. Phys. 104, 3237-3244 (2006). doi:
10.1080/00268970601075246
70. E. Qing, L.A. Viehland, E.P.F. Lee and T.G. Wright,
“Interaction potentials and spectroscopy of Hg+∙Rg and
Cd+∙Rg and transport coefficients for Hg+ and Cd+ in Rg
(Rg = He-Rn)”, J. Chem. Phys. 124, 044316/1–044316/11
(2006). doi: 10.1063/1.2148955
71. T.G. Wright and W.H. Breckenridge, “Radii of atomic ions
determined from diatomic ion-He bond lengths”, J. Phys.
Chem. A 114, 3182–3189 (2010). doi: 10.1021/jp9091927
72. P.J. Linstrom and W.G. Mallard (Eds), NIST Chemistry
Webbook, NIST Standard Reference Database Number
69. National Institute of Standards and Technology,
Gaithersburg, MD, USA, June 2005, http://webbook.nist.
gov.
73. P. Pyykkö, “Predicted chemical bonds between rare
gases and Au+”, J. Am. Chem. Soc. 117, 2067–2070 (1995).
doi: 10.1021/ja00112a021
74. D. Schröder, H. Schwarz, J. Hrušák and P. Pyykkö,
“Cationic gold(I) complexes of xenon and of ligands
containing the donor atoms oxygen, nitrogen, phosphorus and sulfur”, Inorg. Chem. 37, 624–632 (1998). doi:
10.1021/ic970986m
75. J.P. Read and A.D. Buckingham, “Covalency in ArAu+
and related species?”, J. Am. Chem. Soc. 119, 9010–9013
(1997). doi: 10.1021/ja970868y
76. A. Yousef, S. Shrestha, L.A. Viehland, E.P.F. Lee, B.R.
Gray, V.L. Ayles, T.G. Wright and W.H. Breckenridge,
“Interaction potentials and transport properties of coinage metal cations in rare gases”, J. Chem. Phys. 127,
154309/1–154309/10 (2007). doi: 10.1063/1.2774977
77. W.H. Breckenridge, V.L. Ayles and T.G. Wright,
“Evidence for emergent chemical bonding in Au+ -Rg
complexes (Rg = Ne, Ar, Kr and Xe)”, J. Phys. Chem. A 112,
4209-4214 (2008). doi: 10.1021/jp711886a
78. L. Belpassi, I. Infante, F. Tarantelli and L. Visscher,
“The chemical bond between Au(I) and the noble gases.
Comparative study of NgAuF and NgAu+ (Ng = Ar, Kr,
Xe) by density functional and coupled cluster methods”,
J. Am. Chem. Soc. 130, 1048–1060 (2008). doi: 10.1021/
ja0772647
79. P. Zhang, Y. Zhao, F. Hao, X. Song, G. Zhang and Y. Wang,
“Structures and stabilities of Au+Arn (n = 1-6) clusters”,
J. Mol. Struct. (THEOCHEM) 899, 111–116 (2009). doi:
10.1016/j.theochem.2008.12.018
80. M. Velegrakis and Ch. Lüder, “Formation and stability
of singly and doubly charged MgArN clusters”, Chem.
Phys. Lett. 223, 139–142 (1994). doi: 10.1016/00092614(94)00415-3
81. G.S. Fanourgakis and S.C. Farantos, “Potential functions and static and dynamic properties of Mg m+Arn
(m = 1, 2; n = 1-18) clusters”, J. Phys. Chem. 100, 3900–
3909 (1996). doi: 10.1021/jp9514382
82. G.S. Fanourgakis, S.C. Farantos, P. Parneix and Ph.
Bréchignac, “An effective transition state for a complex
cluster isomerization process: comparison between
anharmonic and harmonic models for Mg+Ar12”, J. Chem.
Phys. 106, 4954–4962 (1997). doi: 10.1063/1.474081
83. J. Papadakis, G.S. Fanourgakis, S.C. Farantos and M.
Founargiotakis, “Comparison of line search minimization
algorithms for exploring ­topography of multidimensional
potential energy surfaces: Mg+Arn case”, J. Comput.
454
Chem. 18, 1011–1022 (1997). doi: 10.1002/(SICI)1096987X(199706)18:8<1011::AID-JCC5>3.0.CO;2-W
84. G.S. Fanourgakis, S.C. Farantos, Ch. Lüder, M.
Velegrakis and S.S. Xantheas, “Photofragmentation
spectra and structures of Sr+Arn, n = 2-8 clusters:
experiment and theory”, J. Chem. Phys. 109, 108–120
(1996). doi: 10.1063/1.476527
85. Ch. Lüder, D. Prekas and M. Velegrakis, “Ion-size
effects in the growth sequence of metal-ion doped
noble gas clusters”, Laser Chem. 17, 109–122 (1997). doi:
10.1155/1997/49504
86. D. Prekas, Ch. Lüder and M. Velegrakis, “Structural
transitions in metal ion-doped noble gas clusters:
experiments and molecular dynamics simulations”, J. Chem. Phys. 108, 4450–4459 (1998). doi:
10.1063/1.475856
87. G.E. Froudakis, S.C. Farantos and M. Velegrakis, “Mass
spectra and theoretical modeling of Li+Nen, Li+Arn and
Li+Krn clusters”, Chem. Phys. 258, 13–20 (2000). doi:
10.1016/S0301-0104(00)00175-0
88. S. Bililign, C.S. Feigerle, J.C. Miller and M. Velegrakis,
“Nonstatistical bond breaking in the multi­photon
ionization/­dissociation of [Fe(CO)5]m Arn clusters”, J. Chem.
Phys. 108, 6312–6319 (1998). doi: 10.1063/1.476038
89. M. Velegrakis, G.E. Froudakis and S.C. Farantos,
“Stability and structure of Ni+Arn and Pt+Arn clusters”, J. Chem. Phys. 109, 4687–4688 (1998). doi:
10.1063/1.476856
90. M. Velegrakis, G.E. Foudakis and S.C. Farantos,
“Coordination of Ti cation embedded in argon clusters”,
Chem. Phys. Lett. 302, 595–601 (1999). 10.1016/S00092614(99)00162-1
91. G.E. Froudakis, M. Muhlhauser, S.C. Farantos, A.
Sfounis and M. Velegrakis, Mass spectra and structures
of Cu+Rg n clusters (Rg = Ne, Ar)”, Chem. Phys. 280, 43–51
(2002). doi: 10.1016/S0301-0104(02)00512-8
92. M. Beyer, C. Berg, G. Albert, U. Achatz and V.E.
Bondybey, “Coordinative saturation of cationic niobiumand rhodium-argon complexes”, Chem. Phys. Lett. 280,
459–463 (1997). doi: 10.1016/S0009-2614(97)01203-7
93. J. Hernández-Rojas and D.J. Wales, “Global minima
for rare gas clusters containing one alkali metal
ion”, J. Chem. Phys. 119, 7800–7804 (2003). doi:
10.1063/1.1608852
94. T. Nagata, M. Aoyagi and S. Iwata, “Noble gas clusters
doped with a metal ion. I: ab initio studies of Na+Arn”,
J. Phys. Chem. A 108, 683–690 (2004). doi: 10.1021/
jp036443h
95. C.P. Schulz, P. Claas, D. Schumacher and F.
Stienkemeier , “Formation and stability of high-spin
alkali clusters”, Phys. Rev. Lett. 92, 013401/1–013401/4
(2004). doi: 10.1103/PhysRevLett.92.013401
96. M. Foerste, H. Guenther, O. Riediger, J. Wiebe, G. zu
Putlitz, “Ions and atoms in superfluid helium (4He)”, Z.
Phys. B 104, 317–322 (1997). doi: 10.1007/s002570050456
Review of Gas-Phase Chemistry of Noble Gases
97. Z. Herman, “Dynamics of charge transfer and chemi-
cal reactions of doubly-charged ions at low collision
energies”, Int. Rev. Phys. Chem. 15, 299–342 (1996). doi:
10.1080/01442359609353186
98. S.D. Price, “Interactions of molecular doubly charged
ions with atoms, molecules and photons”, J. Chem.
Soc., Faraday Trans. 93, 2451–2460 (1997). doi: 10.1039/
A700808B
99. F. Grandinetti, “Helium chemistry: a survey of the
role of the ionic species”, Int. J. Mass Spectrom. 237,
243–267 (2004) and references therein. doi: 10.1016/j.
ijms.2004.07.012
100.D.J.D. Wilson and E.I. von Nagy-Felsobuki, “The electronic structure of transition metal dihelide dications”,
Phys. Chem. Chem. Phys. 8, 3399–3409 (2006). doi:
10.1039/B606467A
101.A.J. Page and E.I. von Nagy-Felsobuki, “Structural
and energetic trends in group-I and II hydrohelide cations”, Chem. Phys. Lett. 465, 10–14 (2008). doi: 10.1016/j.
cplett.2008.08.106
102.A.J. Page and E.I. von Nagy-Felsobuki, “Ab ­i nitio
vibrational spectrum of (2 S +) He-MgH2+”, Chem.
Phys. Lett. 468, 299–306 (2009). doi: 10.1016/j.
cplett.2008.12.024
103.N.R. Walker, R.R. Wright, P.E. Barran, H. Cox and
A.J. Stace, “Unexpected stability of (CuAr)2+, (AgAr)2+,
(AuAr)2+ and their larger clusters”, J. Chem. Phys. 114,
5562–5567 (2001). doi: 10.1063/1.1352036
104.G.K. Koyanagi and D.K. Bohme, “Strong closed-shell
interactions: observed formation of BaRg2+ molecules
in the gas phase at room temperature”, J. Phys. Chem.
Lett. 1, 41–44 (2010). doi: 10.1021/jz900009q
105.W.-P. Hu and C.-H. Huang, “The intrinsic stability of the
noble gas-coordinated transition-metal complex ions”,
J. Am. Chem. Soc. 123, 2340–2343 (2001). doi: 10.1021/
ja0033842
106.S. Berski, Z. Latajka and J. Andrés, “The nature of the
Au-Rg bond in the (AuRg4)2+ (Rg = Ar, Kr and Xe) molecules”, Chem. Phys. Lett. 356, 483–489 (2002). doi:
10.1016/S0009-2614(02)00393-7
107.P.D. Carnegie, B. Bandyopadhyay and M.A. Duncan,
“Infrared spectroscopy of Mn+(H2O) and Mn2+(H2O) via
argon complex predissociation”, J. Phys. Chem. A 115,
7602–7609 (2011). doi: 10.1021/jp203501n
108.P.D. Carnegie, B. Bandyopadhyay and M.A. Duncan,
“Infrared spectroscopy of Mn+(H2O) and Mn2+(H2O) via
argon complex predissociation: the charge dependence
of cation hydration”, J. Chem. Phys. 134, 014302/1–
014302/9 (2011). doi: 10.1063/1.3515425
109.E.J. Bieske and O. Dopfer, “High-resolution spectroscopy of cluster ions”, Chem. Rev. 100, 3963–3998 (2000).
doi: 10.1021/cr990064w
110.N.C. Polfer and J. Oomens, “Vibrational spectroscopy
of bare and solvated ionic complexes of biological
­relevance”, Mass Spectrom. Rev. 28, 468–494 (2009). doi:
10.1002/mas.20215
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)455
111.X.-F. Tong, C.-L. Yang, M.-S. Wang, X.-G. Ma and
124.M. Beyer, E.V. Savchenko, G. Niedner-Scatteburg and
D.-H. Wang, “Interactions of Mz-X complexes
(M = Cu, Ag and Au; X = He, Ne and Ar; and z = ± 1)”,
J. Chem. Phys. 134, 024306/1–024306/8 (2011). doi:
10.1063/1.3526955
112.Y. Gao, W. Huang, J. Woodford, L.-S. Wang and X.C.
Zeng, “Detecting weak interactions between Au- and
gas molecules: a photoelectron spectroscopic and ab
initio study”, J. Am. Chem. Soc. 131, 9484–9485 (2009).
doi: 10.1021/ja903043d
113.W. Huang and L.S. Wang, “Probing the 2D to 3D structural transition in gold cluster anions using argon tagging”, Phys. Rev. Lett. 102, 153401 (2009). doi: 10.1103/
PhysRevLett.102.153401
114.W. Huang, S. Bulusu, R. Pal, X.C. Zeng and L.S. Wang,
“Structural transition of gold nanoclusters: from the
golden cage to the golden pyramid”, ACS Nano 3, 1225–
1230 (2009). doi: 10.1021/nn900232d
115.S. Gilb, K. Jacobsen, D. Schooss, F. Furche, R. Ahlrichs
and M.M. Kappes, “Electronic photodissociation spectroscopy of Au n-∙Xe (n = 7-11) versus time-dependent
density functional theory prediction”, J. Chem. Phys. 121,
4619–4627 (2004). doi: 10.1063/1.1778385
116.V. Aquilanti, A. Galli, A. Giardini-Guidoni and G.G.
Volpi, “Ion–molecule reactions in hydrogen-rare gas
mixtures”, J. Chem. Phys. 43, 1969–1973 (1965). doi:
10.1063/1.1697061
117.W.A. Chupka and M.E. Russell, “Photoionization study
of ion-molecule reactions in mixtures of hydrogen and
rare gases”, J. Chem. Phys. 49, 5426–5437 (1968). doi:
10.1063/1.1670068
118.A. Krapp, G. Frenking and E. Uggerud, “Nonpolar
­dihydrogen bonds-On a gliding scale from weak dihydrogen interaction to covalent H-H in symmetric radical
cations [H n E-H-H-EH n]+”, Chem. Eur. J. 14, 4028–4038
(2008). doi: 10.1002/chem.200701613
119.S. Jaksch, F.F. da Silva, S. Denifl, O. Echt, T.D. Märk and
P. Scheier, “Experimental evidence for the existence
of an electronically excited state of the proposed dihydrogen radical cation He-H-H-He +”, Chem. Eur. J. 15,
4190–4194 (2009). doi: 10.1002/chem.200802545
120.O. Mousis, F. Pauzat, Y. Ellinger and C. Ceccarelli,
“Sequestration of noble gases by H3 + in protoplanetary
disks and outer solar system composition”, Astrophys. J.
673, 637–646 (2008). doi: 10.1086/523925
121.M. Bogey, H. Bolvin, C. Demuynck and J.L. Destombes,
“High-resolution rotational spectroscopy of weakly
bound ionic clusters: ArH3 +, ArD 3 +”, Phys. Rev. Lett. 58,
988–991 (1987). doi: 10.1103/PhysRevLett.58.988
122.M. Bogey, H. Bolvin, C. Demuynck, J.L. Destombes and
B.P. Van Eijck, “Tunneling motion in ArH3 + and isotopomers from the analysis of their rotational spectra”, J.
Chem. Phys. 88, 4120–4126 (1988). doi: 10.1063/1.453819
123.K. Hiraoka and T. Mori, “Isotope effect and nature of
bonding in the cluster ions H+3(Ar) n and D+3(Ar) n“, J.
Chem. Phys. 91, 4821–4826 (1989). doi: 10.1063/1.456720
V.E. Bondybey, “Trihydrogen cation solvated by rare gas
atoms: Rg n H3 +”, J. Chem. Phys. 110, 11950–11957 (1999).
doi: 10.1063/1.479134
125.M. Kaczorowska, S. Roszak and J. Leszczynski,
“The structure and properties of H3 +Arn (n = 1–9)
cations”, J. Chem. Phys. 113, 3615–3620 (2000). doi:
10.1063/1.1287831
126.F. Pauzat and Y. Ellinger, “H3 + as a trap for noble gases:
1—The case of argon”, Planet. Space Sci. 53, 1389–1399
(2005). doi: 10.1016/j.pss.2005.07.005
+
127.F. Pauzat and Y. Ellinger, “H3 as a trap for noble
+
gases-2: structure and energetics of XH3 complexes
from X = neon to xenon”, J. Chem. Phys. 127, 014308/1–
014308/13 (2007). doi: 10.1063/1.2746033
128.F. Pauzat, Y. Ellinger, J. Pilmé and O. Mousis, “H 3 +
as a trap for noble gases-3: multiple trapping
of neon, argon and krypton in X n H 3 + (n = 1-3)”, J.
Chem. Phys. 130, 174313/1–174313/15 (2009). doi:
10.1063/1.3126777
129.A. Chakraborty, S. Giri and P.K. Chattaraj, “Trapping of
noble gases (He-Kr) by the aromatic H3 + and Li3 + species: a conceptual DFT approach”, New. J. Chem. 34,
1936–1945 (2010). doi: 10.1039/C0NJ00040J
130.M.C. McCarthy and P. Thaddeus, “High-resolution rotational spectroscopy of NNOH+, DCS +, Ar–D 3 +, Ar–DCO +
and Ar–HN2+”, J. Mol. Spectrosc. 263, 71–77 (2010). doi:
10.1016/j.jms.2010.06.006
131.H. Schöbel, M. Dampc, F. Ferreira da Silva, A.
Mauracher, F. Zappa, S. Denifl, T.D. Märk and P. Scheier,
“Electron impact ionization of CCl4 and SF6 embedded in
superfluid helium droplets”, Int. J. Mass Spectrom. 280,
26–31 (2009). doi: 10.1016/j.ijms.2008.07.009
132.F. Ferreira da Silva, P. Waldburger, S. Jaksch, A.
Mauracher, S. Denifl, O. Echt, T.D. Märk and P.
Scheier, “On the size of ions solvated in helium clusters”, Chem. Eur. J. 15, 7101–7108 (2009). doi: 10.1002/
chem.200802554
133.B. Shepperson, J. Liu, A.M. Ellis and S. Yang,
“Ionization of doped helium nanodroplets: residual
helium attached to diatomic cations and their clusters”, J. Phys. Chem. A 115, 7010–7016 (2011). doi:
10.1021/jp112204e
134.B.E. Callicoatt, D.D. Mar, V.A. Apkarian and K.C. Janda,
“Charge transfer within He clusters”, J. Chem. Phys. 105,
7872–7875 (1996). doi: 10.1063/1.472567
135.M. Fárník and J.P. Toennies, “Ion–molecule reactions in
4
He droplets: flying nano-cryo-reactors”, J. Chem. Phys.
122, 014307/1–014307/11 (2005). doi: 10.1063/1.1815272
136.J.M. Headrick, J.C. Bopp and M.A. Johnson,
“Predissociation spectroscopy of the argon-­
solvated H5O2+ “Zundel” cation in the 1000–1900 cm–1
region”, J. Chem. Phys. 121, 11523–11526 (2004). doi:
10.1063/1.1834566
137.E.G. Diken, J.M. Headrick, J.R. Roscioli, J.C. Bopp, M.A.
Johnson and A.B. McCoy, “Fundamental excitations
456
of the shared proton in the H3O2- and H5O2+ complexes,
J. Phys. Chem. A 109, 1487–1490 (2005). doi: 10.1021/
jp044155v
138.N.I. Hammer, E.G. Diken, J.R. Roscioli, M.A. Johnson,
E.M. Myshakin, K.D. Jordan, A.B. McCoy, X. Huang, J.M.
Bowman and S. Carter, “The vibrational pre­dissociation
spectra of the H5O2+∙RG n (RG = Ar, Ne) clusters: correlation of the solvent perturbations in the free OH
and shared proton transitions of the Zundel ion”, J.
Chem. Phys. 122, 244301/1–244301/10 (2005). doi:
10.1063/1.1927522
139.J.M. Headrick, E.G. Diken, R.S. Walters, N.I. Hammer,
R.A. Christie, J. Cui, E.M. Myshakin, M.A. Duncan,
M.A. Johnson and K.D. Jordan, “Spectral signatures
of hydrated proton vibrations in water clusters”,
Science 308, 1765–1769 (2005). doi: 10.1126/science.1113094
140.L.R. McCunn, J.R. Roscioli, M.A. Johnson and A.B.
McCoy, “An H/D isotopic substitution study of the
H5O2+·Ar vibrational predissociation spectra: exploring
the putative role of Fermi resonances in the bridging
proton fundamentals”, J. Phys. Chem. B 112, 321–327
(2008). doi: 10.1021/jp075289m
141.K. Mizuse and A. Fujii, “Infrared photodissociation
spectroscopy of H+(H2O)6∙M m (M = Ne, Ar, Kr, Xe, H2, N2
and CH4): messenger-dependent balance between H3O+
and H5O2+ core isomers”, Phys. Chem. Chem. Phys. 13,
7129–7135 (2011). doi: 10.1039/C1CP20207C
142.D.J. Miller and J.M. Lisy, “Hydrated alkali-metal cations: infrared spectroscopy and ab initio calculations of
M+(H2O) x=2–5 Ar cluster ions for M = Li, Na, K and Cs”, J.
Am. Chem. Soc. 130, 15381–15392 (2008). doi: 10.1021/
ja803665q
143.A.L. Nicely, D.J. Miller and J.M. Lisy, “Charge and temperature dependence of biomolecule conformations:
K+tryptamine(H2O) n=0–1Arm=0–1 cluster ions”, J. Am. Chem.
Soc. 131, 6314–6315 (2009). doi: 10.1021/ja8094526
144.J.D. Rodriguez and J.M. Lisy, “Infrared spectroscopy
of gas-phase hydrated K+:18-crown-6 complexes: evidence for high energy conformer trapping using the
argon tagging method”, Int. J. Mass Spectrom. 283,
135–139 (2009). doi: 10.1016/j.ijms.2009.02.029
145.S.G. Olesen, T.L. Gausco, G.H. Weddle, S. Hammerum
and M.A. Johnson, “Vibrational predissociation
spectra of Ar-tagged [CH 4∙H 3 O +] binary complex:
spectroscopic signature of hydrogen bonding to
an alkane”, Mol. Phys. 108, 1191–1197 (2010). doi:
10.1080/00268971003698056
146.O. Dopfer, “Spectroscopic and theoretical studies of CH3 + -Rg clusters (Rg = He, Ne, Ar): from weak
intermolecular forces to chemical reaction mechanisms”, Int. Rev. Phys. Chem. 22, 437–495 (2003). doi:
10.1080/0144235031000112878
147.Y.S. Wang, C.H. Tsai, Y.T. Lee, H.C. Chang, J.C. Jiang, O.
Asvany, S. Schlemmer and D. Gerlich, “Investigations
of protonated and deprotonated water clusters using a
Review of Gas-Phase Chemistry of Noble Gases
low-temperature 22-pole ion trap”, J. Phys. Chem. A 107,
4217–4225 (2003). doi: 10.1021/jp022156m
148.M. Baer, D. Marx and G. Mathias, “Theoretical messenger spectroscopy of microsolvated hydronium and
Zundel cations”, Angew. Chem. Int. Ed. 49, 7346–7349
(2010). doi: 10.1002/anie.201001672
149.O. Dopfer, “IR spectroscopic strategies for the structural characterization of isolated and microsolvated
arenium ions”, J. Phys. Org. Chem. 19, 540–551 (2006).
doi: 10.1002/poc.1053
150.S. Chakraborty, A. Patzer and O. Dopfer, “IR spectra of
protonated benzaldehyde clusters, C7H7O+ –L n (L = Ar, N2;
n ≤ 2): ion-ligand binding motifs of the cis and trans oxonium isomers”, J. Chem. Phys. 133, 044307/1–044307/12
(2010). doi: 10.1063/1.3460458
151.T. Jayasekharan and T.K. Ghanty, “Theoretical prediction of HRgCO+ ion (Rg = He, Ne, Ar, Kr and Xe)”,
J. Chem. Phys. 129, 184302/1–184302/8 (2008). doi:
10.1063/1.3008057
152.S. Borocci, N. Bronzolino, M. Giordani and F.
Grandinetti, “Cationic noble gas hydrides-2: A theoretical investigation on HNgHNgH+ (Ng = Ar, Kr, Xe)”,
Comput. Theor. Chem. 964, 318–323 (2011). doi: 10.1016/j.
comptc.2011.01.018
153.S. Borocci, N. Bronzolino, M. Giordani and F.
Grandinetti, “Cationic noble gas hydrides: a theoretical
investigation on the dinuclear HNgFNgH+ (Ng = He-Xe)”,
J. Phys. Chem. A 114, 7382–7390 (2010). doi: 10.1021/
jp102018n
154.J. Lundell and M. Pettersson, “Molecular properties of
Xe2H3 +”, J. Mol. Struct. 509, 49–54 (1999). doi: 10.1016/
S0022-2860(99)00210-0
155.J. Lundell, S. Berski and Z. Latajka, “Density functional
study of the Xe2H3 + cation”, Chem. Phys. 247, 215–224
(1999). doi: 10.1016/S0301-0104(99)00207-4
156.L. Khriachtchev, K. Isokoski, A. Cohen, M. Räsänen and
R.B. Gerber, “A small neutral molecule with two noblegas atoms: HXeOXeH”, J. Am. Chem. Soc. 130, 6114–6118
(2008). doi: 10.1021/ja077835v
157.A. Wada, A. Kikkawa, T. Sugiyama and K. Hiraoka,
“Thermochemical stabilities of the gas-phase cluster ions of halide ions with rare gas atoms”, Int. J.
Mass Spectrom. 267, 284–287 (2007). doi: 10.1016/j.
ijms.2007.02.053
158.B.R. Gray, T.G. Wright, E.L. Wood and L.A. Viehland,
“Accurate potential energy curves for F- -Rg
(Rg = He-Rn): spectroscopy and transport coefficients”,
Phys. Chem. Chem. Phys. 8, 4752–4757 (2006). doi:
10.1039/B610476B
159.N.C. Bera and A.K. Das, “Ab initio study of spectroscopic properties of RgCl (Rg = He, Ne, Ar, Kr) and
their anions”, Mol. Phys. 105, 1433–1439 (2007). doi:
10.1080/00268970701390164
160.C.D. Withers, T.G. Wright, L.A. Viehland, L. Grossman,
C.C. Kirkpatrick and E.P.F. Lee, “Theoretical study of Cl−
RG (rare gas) complexes and transport of Cl− through
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)457
RG (RG = He–Rn)”, J. Chem. Phys. 135, 024312/1–
024312/11 (2011). doi: 10.1063/1.3598472
161.A.A. Buchachenko, R.V. Krems, M.M. Szcze
˛śniak, Y.-D.
Xiao, L.A. Viehland and G. Chałasiński, “Collision and
transport properties of Rg + Cl(2P) and Rg + Cl– (1S)
(Rg = Ar, Kr) from ab initio potentials”, J. Chem. Phys. 114,
9919–9928 (2001). doi: 10.1063/1.1370530
162.A.A. Buchachenko, M.M. Szcze
˛śniak and G. Chałasiński,
“Ab initio zero electron kinetic energy spectroscopy of
the ArCl- and KrCl- anions“, J. Chem. Phys. 114, 9929–
9937 (2001). doi: 10.1063/1.1370531
163.T. Lenzer, I. Yourshaw, M.R. Furlanetto, N.L. Pivonka
and D.M. Neumark, “Zero electron kinetic energy spectroscopy of the XeCl- anion”, J. Chem. Phys. 116, 4170–
4175 (2002). doi: 10.1063/1.1450551
164.A.A. Buchachenko, J. Klos, M.M. Szcze
˛śniak, G.
Chałasiński, B.R. Gray, T.G. Wright, E.L. Wood, L.A.
Viehland and E. Qing, “Interaction potentials for Br – -Rg
(Rg = He-Rn): spectroscopy and transport coefficients”,
J. Chem. Phys. 125, 064305/1–064305/12 (2006). doi:
10.1063/1.2244571
165.A.A. Buchachenko, T.A. Grinev, T.G. Wright and L.A.
Viehland, “Interactions between anionic and neutral
bromine and rare gas atoms”, J. Chem. Phys. 128,
064317/1–064317/14 (2008). doi: 10.1063/1.2830031
166.A.A. Buchachenko, T.V. Tscherbul, J. Klos, M.M.
Szcze˛śniak, G. Chałasiński, R. Webb and L.A. Viehland,
“Interaction potentials of the RG-I anions, neutrals and
cations (RG = He, Ne, Ar)“, J. Chem. Phys. 122, 194311/1–
194311/9 (2005). doi: 10.1063/1.1900085
167.A.H. Jalili, N.S. Matin, L.A. Viheland and M. Shahsavan,
“Determination of HeO + and HeO- interaction potentials
from gaseous ion-mobility data”, Chem. Phys. 365,
94–99 (2009). doi: 10.1016/j.chemphys.2009.10.011
168.L.A. Viehland, R. Webb, E.P.F. Lee and T.G. Wright,
“Accurate potential energy curves for HeO-, NeO- and
ArO-: spectroscopy and transport coefficients”, J.
Chem. Phys. 122, 114302/1–114302/8 (2005). doi:
10.1063/1.1861874
169.A.A. Buchachenko, J. Jakowski, G. Chalasińki, M.M.
Szcze˛śniak and S.M. Cybulski, “Ab initio based study of
the ArO – photoelectron spectra: selectivity of spin-orbit
transitions”, J. Chem. Phys. 112, 5852–5865 (2000). doi:
10.1063/1.481186
170.E. Garand, A.A. Buchachenko, T.I. Yacovitch, M.M.
Szcze˛śniak, G. Chałasiński and D.M. Neumark, “Study
of ArO – and ArO via slow photoelectron velocity-map
imaging spectroscopy and ab initio calculations”, J. Phys.
Chem. A 113, 4631–4638 (2009). doi: 10.1021/jp8113682
171.A.A. Buchachenko, M.M. Szcze
˛śniak, J. Klos and G.
Chałasiński, “Ab initio simulations of the KrO- anion
photoelectron spectra“, J. Chem. Phys. 117, 2629–2634
(2002). doi: 10.1063/1.1491411
172.E. Garand, A.A. Buchachenko, T.I. Yacovitch, M.M.
Szcze
˛śniak, G. Chałasiński and D.M. Neumark, “Study
of KrO- and KrO via slow photoelectron velocity-map
imaging spectroscopy and ab initio calculations”, J. Phys.
Chem. A 113, 14439–14446 (2009). doi: 10.1021/jp903819m
173.T.G. Wright and L.A. Viehland, “Accurate potential
energy curves for HeS-: spectroscopy and transport
coefficients”, Chem. Phys. Lett. 420, 24–28 (2006). doi:
10.1016/j.cplett.2005.12.041
174.E. Garand and D.M. Neumark, “Study of RgS − and RgS
(Rg = Ne, Ar and Kr) via slow photoelectron velocitymap imaging spectroscopy and ab initio calculations”,
J. Chem. Phys. 135, 024302/1–024302/8 (2011). doi:
10.1063/1.3605595
175.S.T. Arnold, J.H. Hendricks and K.H. Bowen,
“Photoelectron spectroscopy of the solvated anion clusters O-(Ar) n=1-26,34: energetics and structure”, J. Chem.
Phys. 102, 39–47 (1995). doi: 10.1063/1.469415
176.J. Jakowski, G. Chałasiński, S.M. Cybulski and M.M.
Szcze˛śniak, “Modeling of the three-body effects in the
Ar2O- trimer from ab initio calculations”, J. Chem. Phys.
118, 2731–2747 (2003). doi: 10.1063/1.1531109
177.J. Jakowski, G. Chałasiński, J. Gallegos, M.W. Severson
and M.M. Szcze˛śniak, “Characterization of Arn O- clusters from ab initio and diffusion Monte Carlo calculations”, J. Chem. Phys. 118, 2748–2759 (2003). doi:
10.1063/1.1531110
178.T. Lenzer, I. Yourshaw, M.R. Furlanetto, N.L. Pivonka
and D.M. Neumark, “Characterization of Arn Cl(-) clusters (n = 2-15) using zero electron kinetic energy and
partially discriminated threshold photodetachment
spectroscopy”, J. Chem. Phys. 115, 3578–3589 (2001).
doi: 10.1063/1.1388202
179.I. Yourshaw, Y. Zhao and D.M. Neumark, “Many-body
effects in weakly bound anion and neutral clusters: zero
electron kinetic energy spectroscopy and threshold
photodetachment spectroscopy of Arn Br- (n = 2–9) and
Arn I- (n = 2–19)”, J. Chem. Phys. 105, 351–373 (1996). doi:
10.1063/1.471893
180.Z. Liu, H. Gomez and D.M. Neumark, “Photoelectron
spectroscopy of clustered transition state precursors
IHI– -Ar and BrHI– -Ar”, Chem. Phys. Lett. 332, 65–72
(2000). doi: 10.1016/S0009-2614(00)01243-4
181.Z. Liu, H. Gomez and D.M. Neumark, “Transition state
spectroscopy of the I + HI reaction in clusters: photoelectron spectroscopy of IHI– –Arn (n = 1–15)”, Faraday
Discuss. 118, 221–232 (2001). doi: 10.1039/B009149I
182.H.B. Lavender and A.B. McCoy, “Transition state
dynamics of Arn (ClHCl) (n = 0-5): effects of complex
formation on the dynamics and spectroscopy”, J. Phys.
Chem. A 104, 644–651 2000. doi: 10.1021/jp993027h
183.I. Adamovic and M.S. Gordon, “Molecular structures
and potential energy surfaces for IHI--Arn (n = 1-7)”, J.
Phys. Chem. A 108, 11042–11048 (2004). doi: 10.1021/
jp040477n
184.N.L. Pivonka, T. Lenzer, M.R. Furlanetto and D.M.
Neumark, “Photoelectron spectroscopy of Xen I− clusters (n ≤ 13)”, Chem. Phys. Lett. 334, 24–30 (2001). doi:
10.1016/S0009-2614(00)01453-6
458
Review of Gas-Phase Chemistry of Noble Gases
185.T. Lenzer, M.R. Furlanetto, N.L. Pivonka and D.M.
198.A.G. Khrapak and W.F. Schmidt, “Negative ions in non-
Neumark, “Zero electron kinetic energy and threshold photodetachment spectroscopy of Xe n I- clusters
(n = 2–14): binding, many-body effects and structures”, J. Chem. Phys. 110, 6714–6731 (1999). doi:
10.1063/1.478577
186.M.T. Zanni, C. Frischkorn, A.V. Davis and D.M. Neumark,
“Dynamics of the charge-transfer-to-solvent states in
I-(Xe) n clusters”, J. Phys. Chem. A. 104, 2527–2530 (2000).
doi: 10.1021/jp9943171
187.I. Becker and O. Cheshnovsky, “Photodetachment
studies of extended excited states in I-Xen clusters
(n = 1–54)”, J. Chem. Phys. 110, 6288–6297 (1999). doi:
10.1063/1.478533
188.I. Becker, G. Markovich and O. Cheshnovsky, “Bound
delocalized excited states in I-Xen clusters”, Phys.
Rev. Lett. 79, 3391–3394 (1997). doi: 10.1103/
PhysRevLett.79.3391
189.Y. Zeiri, “Structure and dynamics of Cl and Br ions and
atoms in Xe clusters”, J. Phys. Chem. A 102, 2785–2791
(1998). doi: 10.1021/jp973179h
190.X. Li, Y. Zhao, X. Jing, F. Liu and F. Hao, “Ab initio study of
Xen I– (n = 1-6) clusters”, Chem. Phys. 328, 64–68 (2006).
doi: 10.1016/j.chemphys.2006.06.013
191.J.H. Hendricks, H.L. de Clercq, C.B. Freidhoff, S.T.
Arnold, J.G. Eaton, C. Fancher, S.A. Lyapustina and J.T.
Snodgrass, “Anion solvation at the microscopic level:
photoelectron spectroscopy of the solvated anion clusters NO – (Y) n, where Y = Ar, Kr, Xe, N2O, H2 S, NH3, H2O
and C2H4(OH)2”, J. Chem. Phys. 116, 7926–7938 (2002).
doi: 10.1063/1.1457444
192.F. Zappa, S. Denifl, I. Mähr, A. Bacher, O. Echt, T.D.
Märk and P. Scheier, “Ultracold water cluster anions”,
J. Am. Chem. Soc. 130, 5573–5578 (2008). doi: 10.1021/
ja075421w
193.F. Ferreira da Silva, S. Jaksch, G. Martins, H. M. Dang,
M. Dampc, S. Denifl, T.D. Märk, P. Limão-Vieira, J. Liu,
S. Yang, A. M. Ellis and P. Scheier, “Electron attachment
and electron ionization of acetic acid clusters embedded in helium nanodroplets”, Phys. Chem. Chem. Phys.
11, 11631–11637 (2009). doi: 10.1039/B918210A
194.F. Ferreira da Silva, S. Denifl, T.D. Märk, N.L. Doltsinis,
A.M. Ellis and P. Scheier, “Electron attachment to formamide clusters in helium nanodroplets”, J. Phys. Chem.
A 114, 1633–1638 (2010). doi: 10.1021/jp909890h
195.F. Ferreira da Silva, S. Denifl, T.D. Märk, A.M. Ellis and
P. Scheier, “Electron attachment to amino acid clusters
in helium nanodroplets: glycine, alanine and serine”,
J. Chem. Phys. 132, 214306/1–214306/6 (2010). doi:
10.1063/1.3429743
196.F.A. Cotton, G. Wilkinson, C.A. Murillo and M. Bochmann,
Advanced Inorganic Chemistry, 6th Edition. John Wiley &
Sons Inc., New York, USA, pp. 1301–1304 (1999).
197.A.G. Khrapak, “Structure of negative impurity ions
in liquid helium”, JETP Lett. 86, 252–255 (2007). doi:
10.1134/S0021364007160072
polar liquids”, Int. J. Mass Spectrom. 277, 236–239 (2008).
doi: 10.1016/j.ijms.2008.04.011
199.E. Coccia, F. Martinetti, E. Bodo and F.A. Gianturco,
“Chemical solutions in a quantum solvent: anionic electrolytes in 4He nanodroplets”, ChemPhysChem 9, 1323–
1330 (2008). doi: 10.1002/cphc.200800132
200.V. Vallet, G.L. Bendazzoli and S. Evangelisti, “Ab initio
study of the ground-state potential of XH- anions (X = He,
Ne, Ar)”, Chem. Phys. 263, 33–40 (2001). doi: 10.1016/
S0301-0104(00)00356-6
201.F. Sebastianelli, C. Di Paola, I. Baccarelli and F.A.
Gianturco, “Quantum and classical structures for 4He
clusters with the H- impurity”, J. Chem. Phys. 119, 8276–
8288 (2003). doi: 10.1063/1.1612477
202.G.M. Begun and R.N. Compton, “Electron collisions with
XeF2”, Int. J. Mass Spectrom. Ion Phys. 30, 379–382 (1979).
doi: 10.1016/0020-7381(79)83015-6
203.I.H. Krouse, C. Hao, C.E. Check, K.C. Lobring, L.S.
Sunderlin and P.G.J. Wenthold, “Bonding and electronic
structure of XeF 3 –“, J. Am. Chem. Soc. 129, 846–852
(2007). doi: 10.1021/ja065038b
204.N. Vasdev, M.D. Moran, H.M. Tuononen, R. Chirakal,
R.J. Suontamo, A.D. Bain and G.J. Schrobilgen, “NMR
spectroscopic evidence for the intermediacy of XeF 3 – in
XeF2 /F− exchange, attempted syntheses and thermo­
chemistry of XeF 3 − salts and theoretical studies of the
XeF 3 − anion”, Inorg. Chem. 49, 8997–9004 (2010). doi:
10.1021/ic101275m
205.K.O. Christe, E.C. Curtis, D.A. Dixon, H.P. Mercier,
J.C.P. Sanders and G.J. Schrobilgen, “The
pentafluoroxenate(IV) anion, XeF 5-: the first example of
a pentagonal planar AX 5 species”, J. Am. Chem. Soc. 113,
3351–3361 (1991). doi: 10.1021/ja00009a021
206.K.O. Christe, D.A. Dixon, J.C.P. Sanders, G.J.
Schrobilgen, S.S. Tsai and W.W. Wilson, “On the structure of the (XeOF 5)- anion of heptacoordinated complex
fluorides containing one or two highly repulsive ligands
or sterically active free valence electron pairs”, Inorg.
Chem. 34, 1868–1874 (1995). doi: 10.1021/ic00111a039
207.A. Ellern and K. Seppelt, “XeOF 5 -, an anion with
pentagonal-­p yramidal structure“, Angew. Chem.
Int. Ed. Engl. 34, 1586–1587 (1995). doi: 10.1002/
anie.199515861
208.M.A.M. Forgeron, R.E. Wasylishen, M. Gerken and G.J.
Schrobilgen, “Solid-state 129Xe and 131Xe NMR study of
the perxenate anion XeO6 4–“, Inorg. Chem. 46, 3585–3592
(2007). doi: 10.1021/ic0624524
209.D.J. Grant, T.-H. Wang and D.A. Dixon, “Heats of formation of XeF 3 +, XeF 3 –, XeF 5 +, XeF 7+, XeF 7– and XeF8 from
high level electronic structure calculations”, Inorg.
Chem. 49, 261–270 (2010). doi: 10.1021/ic901956g
210.Y.-L. Sun, J.-T. Hong and W.-P. Hu, “Theoretical prediction of stable noble-gas anions XeNO2- and XeNO 3- with
very short xenon-nitrogen bond lengths”, J. Phys. Chem.
A 114, 9359–9367 (2010). doi: 10.1021/jp1050904
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)459
211.P. Pyykkö, “Ab initio study of bonding trends among
224.F. Cacace, G. de Petris, F. Pepi, M. Rosi and A. Troiani,
cyanamidophosphates ([PO n (NCN)4-n]3-) and related
systems”, Chem. Eur. J. 6, 2145–2151 (2000). doi:
10.1002/1521-3765(20000616)6:12<2145::AIDCHEM2145>3.0.CO;2-8
212.T.-H. Li, C.-H. Mou, H.-R. Chen and W.-P. Hu,
“Theoretical prediction of noble gas containing anions
FNgO – (Ng = He, Ar and Kr)”, J. Am. Chem. Soc. 127,
9241–9245 (2005). doi: 10.1021/ja051276f
213.Y.-L. Liu, Y.-H. Chang, T.-H. Li, H.-R. Chen and W.-P. Hu,
“Theoretical study on the noble-gas anions F-(NgO) n
(Ng = He, Ar and Kr)”, Chem. Phys. Lett. 439, 14–17 (2007).
doi: 10.1016/j.cplett.2007.03.045
214.S. Borocci, N. Bronzolino and F. Grandinetti, “Noble
gas-sulfur anions: a theoretical investigation of FNgS –
(Ng = He, Ar, Kr, Xe)”, Chem. Phys. Lett. 458, 48–53
(2008). doi: 10.1016/j.cplett.2008.04.098
215.Y. Li, H. Ai, Z. Qi, W. He and L. Zhang, “Stability analysis of the neutral noble gas molecole FNgX and their
anions FNgX– (Ng = He, Ar, Kr; X = O, S)”, Int. J. Quantum
Chem. 109, 782–789 (2009). doi: 10.1002/qua.21895
216.N. Bronzolino, S. Borocci and F. Grandinetti, “Noble
gas-selenium molecular species: a theoretical investigation of FNgSe- (Ng = He-Xe)”, Chem. Phys. Lett. 470,
49–53 (2009). doi: 10.1016/j.cplett.2009.01.037
217.W. Grochala, “On chemical bonding between helium and
oxygen”, Polish J. Chem. 83, 87–122 (2009).
218.P. Antoniotti, N. Bronzolino, S. Borocci, P. Cecchi and F.
Grandinetti, “Noble gas anions: theoretical investigation
of FNgBN– (Ng = He-Xe)”, J. Phys. Chem. A 111, 10144–
10151 (2007). doi: 10.1021/jp0743673
219.F. Bernardi, F. Cacace, G. de Petris, F. Pepi and I. Rossi,
“XeNO 3 +: a gaseous cation characterized by a remarkably strong Xe–0 bond”, J. Phys. Chem. A 102, 5831–5836
(1998). doi: 10.1021/jp980781e
220.M. Attinà, F. Cacace, A. Cartoni and M. Rosi, “Gasphase electrophilic fluorination of methanol by XeF+.
Formation and characterization of protonated methyl
hypofluorite and hypoxenite”, J. Mass Spectrom. 36,
392–396 (2001). doi: 10.1002/jms.140
221.M. Attinà, F. Bernardi, F. Cacace and I. Rossi, “Gaseous
ethylenexenonium ions (C2H4 Xe+) and ethylenefluoroxenonium ions (C2H4 XeF+): a joint mass spectrometric
and theoretical study”, Chem. Eur. J. 5, 1186–1191 (1999).
doi: 10.1002/(SICI)1521-3765(19990401)5:4<1186::AIDCH
EM1186>3.0.CO;2-0
222.F. Cacace, M. Attinà, A. Cartoni and F. Pepi, “Gasphase fluorination of acetilene by XeF+: formation,
structure and reactivity of C 2H2F+ isomeric ions”,
Chem. Phys. Lett. 339, 71–76 (2001). doi: 10.1016/S00092614(01)00248-2
223.M. Attinà, F. Cacace, A. Cartoni and M. Rosi, “Reactivity
of gaseous XeF+ ions with acetonitrile. A joint mass
spectrometric and theoretical study of isomeric
C2H3NF+ and C2H3NXe+ cations”, J. Phys. Chem. A 104,
7574–7579 (2000). doi: 10.1021/jp001823d
“Gaseous trihalogen cations. Formation, structure and
reactivity of Cl 3 + and Cl 2F+ ions from a joint ab initio and
FT-ICR study”, J. Phys. Chem. A 103, 2128–2133 (1999).
doi: 10.1021/jp9841079
225.G. de Petris and A. Ricci, “Experimental evidence for
an asymmetric X 2F 3 + ion in the gas-phase”, Chem.
Phys. Lett. 332, 290–294 (2000). doi: 10.1016/S00092614(00)01256-2
226.F. Pepi, A. Ricci and M. Rosi, “Gas-phase ion chemistry of BF 3 /HN3 mixtures: the first observation of
[BFn N x H n–1]+ (n = 1, 2; x = 1, 3) ions”, J. Phys. Chem. B 110,
4492–4499 (2006). doi: 10.1021/jp0560922
227.I.H. Krouse and P.G. Wenthold, “Bond dissociation
energy and Lewis acidity of the xenon fluoride cation”, Inorg. Chem. 42, 4293–4298 (2003). doi: 10.1021/
ic034301w
228.R. Cipollini and F. Grandinetti, “The gaseous trifluoro­
silylxenon cation, F 3 SiXe+: a stable species with a
silicon-xenon bond”, J. Chem. Soc., Chem. Commun.
773–774 (1995). doi: 10.1039/C39950000773
229.A. Cunje, V.I. Baranov, Y. Ling, A.C. Hopkinson and D.K.
Bohme, “Bonding of rare-gas atoms to Si in reactions
of rare gases with SiF 3 +”, J. Phys. Chem. A 105, 11073–
11079 (2001). doi: 10.1021/jp011908u
230.P. Antoniotti, E. Bottizzo, L. Operti, R. Rabezzana,
S. Borocci and F. Grandinetti, “F 3Ge-Xe +: a xenon-­
germanium molecular species”, J. Phys. Chem. Lett. 1,
2006–2010 (2010). doi: 10.1021/jz100676g
231.L. Operti, R. Rabezzana, F. Turco, S. Borocci, M.
Giordani and F. Grandinetti, “Xenon-nitrogen chemistry:
gas-phase generation and theoretical investigation of
the xenon-difluoronitrenium ion F2N–Xe+”, Chem. Eur. J.
17, 10682–10689 (2011). doi: 10.1002/chem.201101395
232.A. Filippi, A. Troiani and M. Speranza, “Xe0 + and XeOH+
ions: a new class of powerful oxidative oxygenating
agents in the gas phase”, J. Phys. Chem. A 101, 9344–
9350 (1997). doi: 10.1021/jp9718818
233.S.D. Price, M. Manning and S.R. Leone, “Bondforming reactions of gas-phase molecular dications”,
J. Am. Chem. Soc. 116, 8673–8680 (1994). doi: 10.1021/
ja00098a030
234.W. Lu, P. Tosi and D. Bassi, “Bond-forming reactions of
molecular dications with rare gas atoms: production
of ArC2+ in the reaction CO2+ + Ar”, J. Chem. Phys. 112,
4648–4651 (2000). doi: 10.1063/1.481020
235.P.W. Burnside and S.D. Price, “Electron transfer and
bond-forming reactions following collisions of SF2+ with
Ar”, Int. J. Mass Spectrom. 249/250, 279–288 (2006). doi:
10.1016/j.ijms.2005.12.015
236.J. Roithová, R. Thissen, J. Žabka, P. Franceschi, O.
Dutuit and Z. Herman, “Reactions of molecular dications: collision energy dependence of integral crosssections of processes in CHCl 2+ + Ar, D2 systems from
guided beam studies”, Int. J. Mass Spectrom. 228, 487–
495 (2003). doi: 10.1016/S1387-3806(03)00140-4
460
237.J. Roithová, Z. Herman, D. Schröder and H. Schwarz,
“Competition of proton and electron transfers in gasphase reactions of hydrogen-containing dications CHX 2+
(X = F. Cl, Br. I) with atoms, nonpolar and polar molecules”, Chem. Eur. J. 12, 2465–2471 (2006). doi: 10.1002/
chem.200500888
238.D. Ascenzi, P. Tosi, J. Roithová and D. Schröder, “Gasphase synthesis of the rare-gas carbene cation ArCH2+
using doubly ionized bromomethane as a super electrophilic reagent”, Chem. Commun. 4055–4057 (2008). doi:
10.1039/B811115D
239.D. Ascenzi, P. Tosi, J. Roithova, C.L. Ricketts, D.
Schröder, J.F. Lockyear, M.A. Parkes and S.D. Price,
“Generation of the organo-rare gas dications HCCRg2+
(Rg = Ar and Kr) in the reaction of acetylene dications
with rare gases”, Phys. Chem. Chem. Phys. 10, 7121–7128
(2008). doi: 10.1039/B810398D
240.E.-L. Zins, P. Milko, D. Schröder, J. Aysina, D. Ascenzi,
J. Žabka, C. Alcaraz, S.D. Price and J. Roithová,
“Formation of organoxenon dications in the reactions of
xenon with dications derived from toluene”, Chem. Eur. J.
17, 4012–4020 (2011). doi: 10.1002/chem.201002556
241.E.-L. Zins and D. Schröder, “Influence of the structure of medium-sized aromatic precursors on the
reactivity of their dications towards rare gases”, Int.
J. Mass Spectrom. 299, 53–58 (2011). doi: 10.1016/j.
ijms.2010.09.017
242.J.F. Lockyear, K. Douglas, S.D. Price, M. Karkowska,
K.J. Fijalkowski, W. Grochala, M. Remeš, J. Roithová
and D. Schröder, “Generation of the ArCF2 2+ dication”,
J. Phys. Chem. Lett. 1, 358–362 (2010). doi: 10.1021/
jz900274p
243.J. Roithová and D. Schröder, “Silicon compounds of
neon and argon”, Angew. Chem. Int. Ed. 48, 8788–8790
(2009). doi: 10.1002/anie.200903706
244.P. Tosi, R. Correale, W. Lu, S. Falcinelli and D. Bassi,
“Production of the molecular di-cation ArN2+ in the reaction Ar2+ + N2”, Phys. Rev. Lett. 82, 450–452 (1999). doi:
10.1103/PhysRevLett.82.450
245.P. Tosi, W. Lu, R. Correale and D. Bassi, “Production
of the molecular dication ArC2+ by ion-molecule reactions”, Chem. Phys. Lett. 310, 180–182 (1999). doi:
10.1016/S0009-2614(99)00621-1
246.D. Ascenzi, P. Franceschi, P. Tosi, D. Bassi, M.
Kaczorowska and J.N. Harvey, “Bond-forming reactions in dications: production of ArO + and ArO2+ in the
reaction of Ar2+ with O2”, J. Chem. Phys. 118, 2159–2163
(2003). doi: 10.1063/1.1533751
247.N. Lambert, D. Kearney, N. Kaltsoyannis and S.D.
Price, “The bond-forming reactions of atomic dications
with neutral molecules: formation of ArNH+ and ArN+
from collisions of Ar2+ with NH3”, J. Am. Chem. Soc. 126,
3658–3663 (2004). doi: 10.1021/ja038779a
248.V.V. Zelenov, E.V. Aparina, A.V. Loboda, A.S. Kukui, A.F.
Dodonov, S.A. Kashtanov and N.N. Aleinikov, “Mass
spectrometric studies of physical, thermochemical and
Review of Gas-Phase Chemistry of Noble Gases
reactive properties of xenon fluorides, xenon oxides and
xenon oxyfluorides”, Eur. J. Mass Spectrom. 8, 233–246
(2002). doi: 10.1255/ejms.495
249.M.D. Moran, D.S. Brock, H.P.A. Mercier and G.J.
Schrobilgen, “Xe3OF 3 +, a precursor to a noble-gas
nitrate; syntheses and structural characterizations of
FXeONO2, XeF2·HNO 3 and XeF2·N2O 4”, J. Am. Chem. Soc.
132, 13823–13839 (2010). doi: 10.1021/ja105618w
250.N.S. Zefirov, A.G. Gach, V.V. Zhdankin and P.J. Stang,
J. Org. Chem. 56, 1416–1418 (1991). doi: 10.1021/
jo00004a015
251.K. Giles, N.G. Adams and D. Smith, “Reactions of Kr+,
Kr2+, Xe+ and Xe2+ ions with several molecular gases at
300 K”, J. Phys. B: At. Mol. Opt. Phys. 22, 873–883 (1989).
doi: 10.1088/0953-4075/22/6/013
252.S. Seidel and K. Seppelt, “The XeCl+ ion: [XeCl]+[Sb2F11] –
“Angew. Chem. Int. Ed. Engl. 40, 4225–4227 (2001).
doi: 10.1002/1521-3773(20011119)40:22<4225::AIDANIE4225>3.0.CO;2-3
253.F.O. Sladky, P.A. Bulliner, N. Bartlett, B.G. DeBoer and
A. Zalkin, “Xenon difluoride as a fluoride ion donor
and the crystal structure of [Xe2F 3] + [AsF6] –“, Chem.
Commun. (London) 1048–1049 (1968). doi: 10.1039/
C19680001048
254.W.B. Farnham, D.A. Dixon and J.C. Calabrese, “Novel
fluorine-bridged polyfluorinated iodine structures. The
presence of fluorine as the central atom in a five-center,
six-electron bond”, J. Am. Chem. Soc. 110, 8453–8461
(1988). doi: 10.1021/ja00233a022
255.D.A. Dixon, A.J. Arduengo, III and W.B. Farnham,
“Electronic structures of trifluorodixenon(+) and xenon
iodide trifluoride. Examples of 5c,6e hypervalent bonding”, Inorg. Chem. 28, 4589–4593 (1989). doi: 10.1021/
ic00325a011
256.G.L. Smith, H.P.A. Mercier and G.J. Schrobilgen,
“Synthesis of [F 3 SºNXeF][AsF6] and structural study
by multi-NMR and Raman spectroscopy, electronic
structure calculations and X-ray crystallography”, Inorg.
Chem. 46, 1369–1378 (2007) and references therein. doi:
10.1021/ic061899+
257.G.L. Smith, H.P.A. Mercier and G.J. Schrobilgen,
“Ennobling an old molecule: thiazyl trifluoride (NºSF 3),
a versatile synthon for Xe-N bond formation”, Inorg.
Chem. ASAP (2011). doi: 10.1021/ic201161q
258.D.D. DesMarteau, “An unusual xenon cation containing
xenon-nitrogen bonds”, J. Am. Chem. Soc. 100, 6270–
6271 (1978). doi: 10.1021/ja00487a073
259.R. Faggiani, D.K. Kennepohl, C.J.L. Lock and G.J.
Schrobilgen, “The XeN(SO 2 F) 2+ and F[XeN(SO 2 F) 2+] 2+
cations: synthesis, Raman and multinuclear magnetic
­r esonance stdues of the ASF6 – and Sb 3 F16 – compounds and X-ray structures of XeN(S0 2 F) 2+Sb 3 F16 –“,
Inorg. Chem. 25, 563–571 (1988). doi: 10.1021/
ic00224a035
260.G.L. Smith, H.P.A. Mercier and G.J. Schrobilgen,
“F 5 SN(H)Xe +: a rare example of xenon bonded to
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)461
sp 3-hybridized nitrogen; synthesis and structural
­characterization of [F 5 SN(H)Xe][AsF6]”, Inorg. Chem. 47,
4173–4184 (2008). doi: 10.1021/ic702039f
261.B. Fir, J.M. Whalen, H.P.A. Mercier, D.A. Dixon and G.J.
Schrobilgen, “Syntheses of [F 5 TeNH 3][AsF6], [F 5 TeN(H)
Xe][AsF6] and F 5 TeNF 2 and characterization by multiNMR and Raman spectroscopy and by electronic
structure calculations: the X-ray crystal structures of
a- and b-F 5 TeNH2 , [F 5 TeNH 3][AsF6] and [F 5 TeN(H)Xe]
[AsF6]”, Inorg. Chem. 45, 1978–1996 (2006). doi: 10.1021/
ic051451t
262.G.L. Smith and G.J. Schrobilgen, “On the reactivity of
F 3 SºNXeF+: syntheses and structural characterizations of [F4 S=N–Xe---NºSF 3][AsF6], a rare example of a
N–Xe–N linkage and [F 3 S(NºSF 3)2][AsF6]”, Inorg. Chem.
48, 7714–7728 (2009). doi: 10.1021/ic900651n
263.G.L. Smith, H.P.A. Mercier and G.J. Schrobilgen, “Solidstate and solution rearrangements of F 3 SºNXeF+ leading to the F4 S=NXe+ cation; syntheses, HF solvolyses
and structural characterizations of [F4 S=NH2][AsF6]”,
J. Am. Chem. Soc. 131, 7272–7286 (2009). doi: 10.1021/
ja901187n
264.K. Koppe, H.-J. Frohn, H.P.A. Mercier and G.J.
Schrobilgen, “[C6F 5 Xe]+ and [C6F 5 XeNCCH3]+ salts of the
weakly coordinating borate anions, [BY4]- (Y = CN, CF 3, or
C6F 5)”, Inorg. Chem. 47, 3205–3217 (2008). doi: 10.1021/
ic702259c
265.H.J. Frohn, T. Schroer and G. Henkel, “Coordinative
behavior of the pentafluorophenylxenonium salt
[C6F 5 Xe]+[AsF6] – to pyridines of different basicity”, Z.
Naturforsch. B 50, 1799–1810 (1995).
266.D.D. DesMarteau, R.D. LeBlond, S.F. Hossain and
D. Nothe, “Xenon-nitrogen bonds. The synthesis
and characterization of [imidobis(sulfuryl fluoride)]
xenon(II) derivatives Xe[N(SO2F)2]2, FXeN(SO2F)2 and
[(FSO2)2NXe]2F+AsF6- and the radical ∙N(SO2F)2”, J.
Am. Chem. Soc. 103, 7734-7739 (1981). doi: 10.1021/
ja00416a007
267.D. Holtz and J.L.Beauchamp, “Xenon as a nucleophile
in gas-phase displacement reactions: formation of the
methyl xenonium ion”, Science 173, 1237–1238 (1971).
doi: 10.1126/science.173.4003.1237
268.G.R. Hertel and W.S. Koski, “Ion–molecule reactions
between rare gas ions and methane”, J. Am. Chem. Soc.
87, 1686–1691 (1965). doi: 10.1021/ja01086a012
269.T.O. Tiernan and P.S. Gill, “Investigation of ionic reactions in the xenon-methane system using a tandem
mass spectrometer”, J. Chem. Phys. 50, 5042–5044
(1969). doi: 10.1063/1.1671011
270.D. Naumann and W. Tyrra, “The first compound with
a stable xenon-carbon bond: 19F- and 129Xe-n.m.r.
spectroscopic evidence for pentafluorophenylxenon(II)
fluoro­borates”, J. Chem. Soc., Chem. Commun. 47–50
(1989). doi: 10.1039/C39890000047
271.H.J. Frohn and S. Jakobs, “The pentafluorophenyl­
xenon(II) cation: [C6F 5 Xe]+; the first stable system with
a xenon-carbon bond”, J. Chem. Soc., Chem. Commun.
625–627 (1989). doi: 10.1039/C39890000625
272.H.J. Frohn, S. Jacobs and G. Henkel, “The
acetonitrile(pentafluorophenyl)xenon(II) cation,
[MeCN-Xe-C 6 F 5] +: the first structural characterization of a xenon-carbon bond”, Angew. Chem.
Int. Ed. Engl. 28, 1506–1507 (1989). doi: 10.1002/
anie.198915061
273.H.J. Frohn and V.V. Bardin, “Preparation and reactivity of compounds containing a carbon-xenon bond”,
Organometallics 20, 4750–4762 (2001). doi: 10.1021/
om010490j
274.H. Basch, T. Hoz and S. Hoz. “Hyperconjugative effects
in carbenium and silicenium ions”, J. Phys. Chem. A 103,
6458–6467 (1999). doi: 10.1021/jp991083c
275.S.A. Miller, H. Luo, S.J. Pachuta and R.G. Cooks,
“Soft-landing of polyatomic ions at fluorinated self-­
assembled monolayer surfaces”, Science 275, 1447–
1450 (1997). doi: 10.1126/science.275.5305.1447
276.H. Luo, S.A. Miller, R.G. Cooks and S.J. Pachuta, “Soft
landing of polyatomic ions for selective modification of
fluorinated self-assembled monolayer surfaces”, Int. J.
Mass Spectrom. Ion Processes 174, 193–217 (1998). doi:
10.1016/S0168-1176(97)00302-9
277.B. Feng, J. Shen, V. Grill, C. Evans and R.G. Cooks,
“Cleavage of C–C and C–F bonds by Xe +. and I+ ions in
reactions at a fluorinated self-assembled monolayer
surface: collision energy dependence and mechanisms”,
J. Am. Chem. Soc. 120, 8189–8198 (1998). doi: 10.1021/
ja973201k
278.P. Antoniotti, E. Bottizzo, L. Operti, R. Rabezzana, S.
Borocci and F. Grandinetti, “Gas-phase chemistry of
ionized and protonated GeF4: a joint experimental and
theoretical study”, J. Mass Spectrom. 46, 465–477 (2011).
doi: 10.1002/jms.1913
279.P. Pykkö and M. Atsumi, “Molecular single-bond covalent radii for elements 1-118. Chem.-Eur. J. 15, 186–197
(2009). doi: 10.1002/chem.200800987
280.Z. Lv, G.-H. Chen, D. Li, D. Wu, X.-C. Huang, Z.-R. Li
and W.-G. Liu, “RgBF2+ complexes (Rg = Ar, Kr and Xe):
the cations with large stabilities”, J. Chem. Phys. 134,
154302/1–154302/8 (2011). doi: 10.1063/1.3572224
281.T.-Y. Lin, J.-B. Hsu and W.-P. Hu, “Theoretical prediction of new noble-gas molecules OBNgF (Ng = Ar, Kr and
Xe)”, Chem. Phys. Lett. 402, 514–518 (2005). doi: 10.1016/j.
cplett.2004.12.090
282.Z. Herman, J. Žabka, Z. Dolejšek and M. Fárník,
“Dynamics of chemical and charge transfer reactions
of molecular dications: beam scattering and total
cross section data on CF 2D + (CF 2H+), CF 2+ and CF+
formations in CF 2 2+ + D2(H2) collisions”, Int. J. Mass
Spectrom. 192, 191–203 (1999). doi: 10.1016/S13873806(99)00092-5
283.L. Mrázek, J. Žabka, Z. Dolejšek, J. Hrušák and Z.
Herman, “Dynamics of chemical and charge-transfer
reactions of molecular dications: III. Beam scattering
462
and total cross section data for processes in the system
CO2 2+ + D2, J. Phys. Chem. A 104, 7294–7303 (2000). doi:
10.1021/jp0011645
284.L.D. Landau, “On the theory of transfer of energy at collisions II”, Phys. Z. Sowjetunion 2, 46 (1932).
285.C. Zener, “Non-adiabatic crossing of energy levels”,
Proc. R. Soc. Lond. Ser. A 137, 696–702 (1932). doi:
10.1098/rspa.1932.0165
286.G. Frenking, W. Koch, F. Reichel and D. Cremer, “Light
noble gas chemistry: structures, stabilities and
bonding of helium, neon and argon compounds”, J.
Am. Chem. Soc. 112, 4240–4256 (1990). doi: 10.1021/
ja00167a020
287.N. Tafadar, N. Kaltsoyannis and S.D. Price, “Electrontransfer and neutral-loss reactions in collisions of CF 32+
with argon”, Int. J. Mass Spectrom. 192, 205–214 (1999).
doi: 10.1016/S1387-3806(99)00093-7
288.W.P. Hu, S.M. Harper and S.D. Price, “The dynamics
and kinematics of the electron transfer reactions of
CF 32+ with Ar”, Mol. Phys. 103, 1809–1889 (2005). doi:
10.1080/00268970544798
289.Y.-Y. Lee, S.R. Leone, P. Champkin, N. Kaltsoyannis and
S.D. Price, “Laser photofragmentation and collisioninduced reactions of SiF2 2+ and SiF 32+”, J. Chem. Phys.
106, 7981–7994 (1997). doi: 10.1063/1.473809
290.P. Champkin, N. Kaltsoyannis and S.D. Price, “A
theoretical investigation of the electron-transfer
Review of Gas-Phase Chemistry of Noble Gases
r­ eactions of the SiF 3 2+ dication with the rare gases,
neon, argon, krypton and xenon”, Int. J. Mass Spectrom.
Ion Processes 172, 57–69 (1998). doi: 10.1016/S01681176(97)00243-7
291.P. Tosi, R. Correale, W. Lu and D. Bassi, “Production
of ArN+ ions in the reactions Ar+ + N2 and
N2+ + Ar”, J. Chem. Phys. 110, 4276–4279 (1999). doi:
10.1063/1.478311
292.M.A. Vincent and I.H. Hillier, “Ab initio calculations of
the potential-energy curves of the low-lying states
of NeC 2+, ArC 2+, NeO2+ and ArO2+”, J. Chem. Soc.,
Faraday Trans. 2 84, 1229–1236 (1988). doi: 10.1039/
F29888401229
293.M.W. Wong and L. Radom, “Multiply bonded argoncontained ions: structures and stabilities of XArn+ cations (X = B, C, N; n = 1-3)”, J. Phys. Chem. 93, 6303–6308
(1989). doi: 10.1021/j100354a009
294.P. Jonathan, A.G. Brenton, J.H. Beynon and R.K. Boyd,
“Characterisation of cluster ions formed from inert
gas atoms plus small molecules and radicals”, Int. J.
Mass Spectrom. Ion Processes 71, 257–282 (1986). doi:
10.1016/0168-1176(86)80035-0
295.D.J. Levandier and Y.-H. Chiu, “A guided-ion beam study
of the reactions of Xe+ and Xe2+ with NH3 at hyperthermal collision energies”, J. Chem. Phys. 133, 154304/1–
154304/8 (2010). doi: 10.1063/1.3488055
Biographic details
Felice Grandinetti graduated in
Chemistry cum laude in 1985 at the
University of Rome La Sapienza.
After working as a Researcher of the
Italian CNR (1988-1992), he became
Associate (1992), and afterwards
Full Professor (2000) of General and
Inorganic Chemistry at the University
of Viterbo. His research activity,
performed also in collaboration with various italian and
foreign Institutions, has been constantly devoted to the theoretical and experimental study of the gas-phase chemistry of
simple inorganic species, mostly ionic. Typically investigated
topics include the formation of novel ions, the characterization
of their structure, bonding, and spectroscopic properties, and
the investigation of their gas-phase reactivity. The continuing
interest focused in particular on species containing the noble
gases arises not only from the challenging problems posed
by the chemical inertness of these elements, but also from
issues related with the use of noble-gas matrices and superfluid helium as environments to study the structure and reactivity of molecules and ions.
The quarter of San Pellegrino. The historical center of Viterbo,
enclosed in a town wall, dates back to the middle age. It still
maintains an evocative aspect made of ancient churches, tight
and tortuous roads, arches, and external staircases. The oldtown heart is the quarter of San Pellegrino. Every year, in the
spring, it colors in a spectacular way thanks to a suggestive
decking with flowers.
F. Grandinetti, Eur. J. Mass Spectrom. 17, 423–463 (2011)463
The Palace of the Popes. Viterbo is also known as the Town of
the Popes. They resided there in particular in the second half
of the thirteenth century, and their presence strongly favored
the flourishing of the medieval center. The Palace of the Popes
(1267) still remains the symbol of the city.
The University. The University of Viterbo (La Tuscia) was
founded in 1979. Its main building is placed in the center of the
town, and belongs to the architectural complex of Santa Maria
in Gradi. It still maintains characteristic elements such as
cloisters and fountains.
The Bulicame. Viterbo is also famous for its hot springs of sulphureous nature. In a typical area, called Bulicame, one can dive in these
waters, and benefit from their healing properties. The place is also mentioned by Dante Alighieri in his Divina Commedia.