Download Fourier Transform Microwave Spectrometer with Double Resonance


Part 1
The Cavity FTMW Spectrometer with Double
Resonance
Application of Double Resonance

Part2
Formic and Propiolic Acid Dimer
 Part 3
Trans Methyl Formate
The FTMW Spectrometer
is powerful tool used in
rotational spectroscopy,
it is used to determine
molecular structure by
observing the rotational
transitions in the
microwave spectrum.
Balle, T.J.; Flygare, W.H. Fabry–Perot cavity pulsed Fourier
transform microwave spectrometer with a pulsed nozzle
particle source. Rev. Sci.Instrum. 1981, 52 (1), 33–45.
Narrow Band (Cavity)
Chirped Broadband Spectrometer
Advantage
Advantage
Disadvantage
Enhanced Signal Slow for large
bandwidth
Large Frequency
Range
More power
Polarizing Pulse,
more power
Multiple gas nozzle
Loss of signal
Disadvantage
Narrow
Bandwidth
Amplification of
Emission
Expensive
electronics
In expensive
Highly reliant on
Phase stability
Fast for
monitoring one
line
Wolfgang Jaeger, University of Alberta
1. Pulse molecular beamAdiobatic expansion
occurs which cools the
molecules
2. MW pulse - Polarizes the
molecules at Resonant
Transition
3. Polarized gas coherently
emits at resonant
frequencies
4. Signals detected in
superheterodyne
detector and a Fourier
Transform is done to give
Spectrum
http://www.chem.ualberta.ca/~jaeger/research/ftmw/ftmw.htm
A Rotational Transition is monitored.
2. Cavity is scanned with a second
frequency that is resonant with
monitored state. Coherence is
destroyed if the second frequency
shares a similar quantum state with the
monitored frequency.
3. This coherence disruption is shown by a
depletion in intensity.
1.
505
Linked Map
of
Quantum
States
404
303
202
515
414
313
212
413

Frequency Range Extension

Checking assignment of rotational
spectra of molecules which helps to
identify molecules.
Double
Resonance
Monitor- A-Type 16430 MHz
Scan- B-type 15498.34MHz
and the quantum mechanics behind tunneling
Carboxylic Acid Dimer Formation
•Investigation of the acid dimer formation
by understanding the tunneling motion of
the hydrogen bonds.
•The use of the cavity and double
resonance will help identify the weaker Btype transitions on an already weak dipole
since it has a weak dipole of .08 D.
•The B-type transitions are important to
monitor, because they allow the tunneling
rate to be calculated.
•By understanding the rate of proton
tunneling, hydrogen bonds in biological
systems can be better understood.
Applications
•Understand the rate of tunneling in the
hydrogen bond.
•Signaling mechanisms in bio-systems; proteins
and enzymes.
• The hydrogen bonds that make up DNA.
Acid Dimer Formation
X
Y
Formic Acid
The rate at which the two
protons tunnel across creates
the hydrogen bond and the
dimer formation.
X
Y
Propiolic Acid
Tunneling Motion: Classics vs. Quantum
Classically the motion of
a particle through a
barrier suggests that
given a certain energy it
would not be able to
pass though it.
According to quantum mechanics
the wave like nature of particles
allows them to pass through
barriers. The lower the barrier the
less the particles have to go
through and the greater chance of
passing though. This is called
tunneling.
H
H
EHydrogen < EBarrier
Only part of the wave makes it though.
Left Potential Well
X
Y
E
Right Potential Well
X
Y
E
Tunneling
E
E
Symmetric Double Well
Tunneling
E
E
O- Asymmetric
O+ Symmetric
The wave functions of the two different
forms interact to give the splitting
according to quantum mechanics.
Vibrational Transitions from the Tail
EE
•Even though there is splitting, the transitions
between the splitting can not always be observed.
•The dimer has a long chain on the propiolic acid
which allows it to have a change in dipole as the
tunneling process takes place.
•The change in dipole allows there to be some
vibrational transitions going from the O+ to the Ostates.
•The end result: splitting occurs from the predicted
frequency on the spectrometer.
•The rate of tunneling can be calculated by the
amount of splitting.
A
A
O- Asymmetric
O+ Symmetric
Addition of Deuterated Form
•The use of the deuterated form of
the dimer causes the mass that
undergoes tunneling to change from
2 amu to 4 amu and lowers the rate
of tunneling.
EE
•The zero point energy of the dimer
lowers and also causes the tunneling
rate to slow.
•The addition of the deuterium lowers
the rate by about 67 times.
Normal Acid Dimer
Deuterated Acid Dimer
Hydrogens
Normal Form
Deuteriums
Deuterated Form
Procedure: Set up
•Cavity was equipped with
a reservoir to hold the acids
instead of being inside of a
gas tank.
•Neon gas was passed over
the sample to deliver the
molecules into the
chamber.
•A 1:2 ratio of formic to
propiolic acid was used.
Procedure: Frequencies
Deuteriums
Calculated Frequencies
Formic (OD)-Propiolic (OH)
505-404
8585.926 MHz
606-505
10278.184 MHz
Formic (OH)-Propiolic (OD)
505-404
8567.293 MHz
606-505
10256.123 MHz
Formic (OD)-Propiolic (OD)
505-404
8540.464 MHz
606-505
10222.995 MHz
Double Resonance
515-404
12613.528 MHz
615-505
14001.597 MHz
While monitoring the double
deuterated 606 to 505
transition at 10222.99 MHz,
double resonance was used
to investigate a few MHz
away from the predicted
center.
Results
Calculated Frequencies
Formic (OD)-Propiolic (OH)
505-404
8585.926 MHz
606-505
10278.184 MHz
Formic (OH)-Propiolic (OD)
505-404
8567.293 MHz
606-505
10256.123 MHz
Formic (OD)-Propiolic (OD)
505-404
8540.464 MHz
606-505
10222.995 MHz
Double Resonance
515-404
12613.528 MHz
615-505
14001.597 MHz
Predicted: 14001.597 MHz
The splitting occurred
14005.0 MHz and
13998.2 MHz
While monitoring the 606 to 505
transition at 10222.99 MHz,
double resonance was used
to investigate a few MHz
away from the predicted
center.
•The predicted
splitting about 3.4 MHz
away for the double
deuterated form.
•From prior
experiments the pure
hydrogen form, the
splitting occurred 291
MHz away.
•To confirm this
hypothesis the 717 to
606 transition was
investigated.
Conclusion
•The slitting occurs about 3.4 MHz
from the predicted frequency for
the double deuterated form.
•The higher the activation barrier
the more difficult for the dimer to
tunnel.
•A change in mass that undergoes
tunneling will effect the tunneling
motion.
•The H-C ≡C- allows there to be
transitions between the vibrational
states of the splitting.
3.4 MHz
Predicted
Quantum Splitting
E E
Deuteriums
Normal Acid Dimer
Deuterated Acid Dimer

Overall Goal of CCU &
Summer Research

High Abundance of MF
in space.
Spatial Map of Orion Nebula*

Horn et al. (2004)** propose following reaction
pathways
[CH3OH2]+ + H2CO  [HC(OH)OCH3]+ + H2
H2C=O + [H2C=O-H]+  [HC(OH)OCH3]+ + hv
[CH3OH2]+ + CO  [HC(OH)OCH3]+ + hv
CH3+ + HCOOH  [HC(OH)OCH3]+ + hv

Probable Reaction: [CH3OH2]+ + HCOOH  HC(OH+)OCH3
*S.-Y. Liu, J.M. Girart, A. Remijan, and L.E. Snyder, Ap.J.,
576 (2002) 255-263.
**A. Horn et al., Ap.J., 611 (2004) 605-614
+ H2O
trans
µa = 4.1 D (ab initio)
µb = 2.8 D (ab initio)
A = 47354.28 MHz
B = 4704.440 MHz
C = 4398.435 MHz
V3 = 14.9 cm-1
cis
µa = 1.63 D (Bauder 1979)
µb = 0.68 D (Bauder 1979)
A = 19985.71 MHz (Curl 1959)
B = 6914.63 MHz (Curl 1959)
C = 5304.47 MHz (Curl 1959)
V3 = 398.76 cm-1 (Oesterling et al 1998)
Green: Monitored
Frequencies
Yellow: Second
Scanning
Frequencies

Four methods of identifying trans lines in
the lab & in space:
1. Do the lines belong to the same species?
2. Do the lines appear in the Broadband
spectrum?
3. Are the experimental data & ab initio a
good fit?
4. Do the lines appear in space?
DR
Monitored
Monitored
DR
Parameter
Experimental
Ab Initio
A (MHz)
47357(320)
46543.42
B (MHz)
4704.44(6)
4732.99
C (MHz)
4398.434(1)
4417.46
ΔJ(kHz)
1.1(1)
ΔJK (kHz)
-124(9)
δJ (kHz)
0.108(5)
ΔKm (MHz)
-163(61)
ΔJm (MHz)
0.92(8)
δm (MHz)
-1.6(6)
V3 (cm-1)
14.9(6)
22.6
θtop (deg)a
23.49(16)
26.0
Iα (amu Å2)
3.18(6)
3.149
Nlines
28
rms error (kHz)
35
Fit with XIAM
H. Hartwig and H. Dreizler, Z. Naturforsch 51a
(1996) 923-932.
Temperature (K)
Detection of trans-Methyl Formate in
Sagitarius-B2(N)
Green Bank Telescope PRIMOS Project, available on the Internet at http://www.cv.nrao.edu/~aremijan/PRIMOS.
Double Resonance is an effective
technique in identifying weak transitions.
 Double Resonance can be used in
understanding tunneling in Carboxlyic
Acid Dimers.
 Trans-Methyl Formate is found in Space!

1.
2.
3.
4.
5.
D.A. Andrews, J.G. Baker, B.G. Blundell and
G.C. Petty, 3. Mol. Stmcr., 97, 1983, 271-83.
T.J. Balle, W.H. Flygare, Rev. Sci. Instrum.
1981, 52 (1), 33–45.
A. Bauder, M. et al., Chemical Physics
Letters, 144, 1988, 2.
J. Ekkers and W.H. Flygare, Rev. Sci. Instr. 47,
1976, 448.
K.O. Douglass, New FTMW Techniques for
DRS. Thesis. University of Virginia, 2007.
Personal Thanks to:
 Brooks Pate
 Matt Muckle
 Justin Neill
 Amanda Steber
NSF Division of Human
Resource
Development
Louis Stokes Alliance
for Minority
Participation program
(HRD-0703554)
NSF Division of
Chemistry
Centers for Chemical
Innovation program
(CHE-0847919)
Brooks Pate
Matt Muckle
Sara Fitzgerald
Justin Neill
Amanda Steber
Danny Zaleski
Marcus Martin
Kristin Morgan
Shirley Cauley
Anthony Remijan
Robin Pulliam