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Infrared Spectroscopy of
Protonated Methanol-Water Clusters
-Effects of Heteromolecules in Hydrogen Bond NetworkKen-ichiro Suhara, Asuka Fujii and Naohiko Mikami
Department of Chemistry, Graduate School of Science,
Tohoku University
Introduction
Hydrogen bond networks
in large-size protonated clusters
Microscopic models for
1. local structures in protic solvent
2. proton motion in condensed phases
IR photodissociation spectroscopy of OH-stretching vibrations
Size-dependent development of the hydrogen bond
network structures in large-size clusters
Size dependence of
hydrogen bond
network structures
H+(H2O)n
chain
n < ~10
net
~10 < n
cage
21 ≤ n
Miyazaki et al., Shin et al. (2004)
H+(MeOH)n
n=7
The bicyclic structure formation is completed at n = 7
The terminal of network development
More complicated cage structures
can not be formed (n > 7)
Methanol molecule
Chang et al., and Fujii et al.
(1999&2005)
･3-coordination at the maximum
･Donation of only one proton
Strictly
restricted structure !
Totally different preferences between
the hydrogen bond networks of water and methanol
Structures in the protonated
water-methanol mixed clusters ?
Previous study
M3W1
H+(MeOH)n(H2O)m , m + n = 4
IR spectroscopy and DFT calculations
Coexistence of H3O+ and CH3OH2+ ion cores
Wu et al., J. Phys. Chem. A. 2004.
Mass spectrometry for H+(MeOH)n(H2O)m
Presence of magic numbers
n = 9, m = 1 & n = 10, m = 2
Proton switching
from the alcohol to the water site
at n = 9, m = 1 & n = 10, m = 2 ?
Garvey et al., J. Am. Chem. Soc. 1992.
Garvey et al., J. Phys. Chem. A. 2000.
This study
A structural analysis of protonated
water-methanol mixed clusters
H+(MeOH)n(H2O)m, (n = 2 - 13, m = 1 & 2)
by IR spectroscopy
Hydrogen bond network including heteromolecules
Mass spectrometry
Ion intensity
Ion intensity
H+(MeOH)n(H2O)1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
size(n+m)
8
9
10
11
size n
Garvey et al., J. Am. Chem. Soc. 1992.
No magic number…
7
magic
number
12
The magic number
was not observed
in our mass spectrum
13
Proton switching?
IR spectra of H+(MeOH)n(H2O)m, (m = 0, 1)
m=0
n=4
m=1
n=3
5
4
6
5
7
6
8
7
9
8
10
11
9
10
12
11
13
12
14
13
15
Disappearance
of free OH peaks
n>7: similar IR spectra
to H+(MeOH)n+1
No drastic change of
the IR spectra at n = 7 - 9
No evidence
for proton switching
H+(MeOH)n(H2O)1
Definition
of symbols
Disappearance of
the free OH band in n > 6
n=3
n=3
4
n=4
n=5
5
Free OH
6
7
Free OH
8
9
10
n=6
n=7
11
12
13
bicyclic structure
tricyclic structure
Conclusion
IR spectroscopy of H+(MeOH)n(H2O)m, (m = 1 & 2)
No magic number in the mass distribution
No spectroscopic evidence for the proton switching
Structural convergence to the tricyclic structure for m = 1