Part 1 Application of Double Resonance Presentation_SpectrometerGroup.pdf · Application of Double...
Transcript of Part 1 Application of Double Resonance Presentation_SpectrometerGroup.pdf · Application of Double...
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 Disadvantage Advantage Disadvantage
Enhanced Signal Slow for large
bandwidth
Large Frequency
Range
More power
Polarizing Pulse,
more power
Narrow
Bandwidth
Multiple gas nozzle Loss of signal
Amplification of
Emission
Expensive
electronics
In expensive Highly reliant on
Phase stability
Fast for
monitoring one
line
http://www.chem.ualberta.ca/~jaeger/research/ftmw/ftmw.htm
Wolfgang Jaeger, University of Alberta
1. Pulse molecular beam-
Adiobatic 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
1. 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.
Frequency Range Extension
Checking assignment of rotational
spectra of molecules which helps to
identify molecules.
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 B-type 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.
Y
X
Formic Acid Propiolic Acid
X
Y
The rate at which the two
protons tunnel across creates
the hydrogen bond and the
dimer formation.
Acid Dimer Formation
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.
Only part of the wave makes it though.
H
H
EHydrogen < EBarrier
The wave functions of the two different
forms interact to give the splitting
according to quantum mechanics.
O-
+O
Asymmetric
Symmetric
E
Symmetric Double Well
Tunneling
E
E
•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 O-
states. •The end result: splitting occurs from the predicted frequency on the spectrometer. •The rate of tunneling can be calculated by the amount of splitting.
O-
O+
Asymmetric
Symmetric
A
A
Vibrational Transitions from the Tail
E
E
•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.
•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.
Deuteriums
Normal Form Deuterated Form
Addition of Deuterated Form
Normal Acid Dimer
Deuterated Acid Dimer
Hydrogens
E
•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: Set up
Procedure: Frequencies
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.
Deuteriums
Results
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.
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
The splitting occurred
14005.0 MHz and
13998.2 MHz
Predicted: 14001.597 MHz
•The predicted
splitting about 3.4 MHz
away for the double
deuterated form.
•To confirm this
hypothesis the 717 to
606 transition was
investigated.
•From prior
experiments the pure
hydrogen form, the
splitting occurred 291
MHz away.
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
E
Predicted
Quantum Splitting
Deuteriums
Normal Acid Dimer
E
Deuterated Acid Dimer
Overall Goal of CCU & Summer Research
High Abundance of MFin space.
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 + H2O
*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
Spatial Map of Orion Nebula*
cisµa = 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)
transµa = 4.1 D (ab initio)
µb = 2.8 D (ab initio)A = 47354.28 MHzB = 4704.440 MHz C = 4398.435 MHzV3 = 14.9 cm-1
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?
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) 35Fit with XIAM
H. Hartwig and H. Dreizler, Z. Naturforsch 51a
(1996) 923-932.
Green Bank Telescope PRIMOS Project, available on the Internet at http://www.cv.nrao.edu/~aremijan/PRIMOS.
Tem
pe
ratu
re (
K)
Detection of trans-Methyl Formate in
Sagitarius-B2(N)
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. D.A. Andrews, J.G. Baker, B.G. Blundell and G.C. Petty, 3. Mol. Stmcr., 97, 1983, 271-83.
2. T.J. Balle, W.H. Flygare, Rev. Sci. Instrum. 1981, 52 (1), 33–45.
3. A. Bauder, M. et al., Chemical Physics Letters, 144, 1988, 2.
4. J. Ekkers and W.H. Flygare, Rev. Sci. Instr. 47, 1976, 448.
5. K.O. Douglass, New FTMW Techniques for DRS. Thesis. University of Virginia, 2007.
Brooks Pate
Matt Muckle
Sara Fitzgerald
Justin Neill
Amanda Steber
Danny Zaleski
Marcus Martin
Kristin Morgan
Shirley Cauley
Anthony Remijan
Robin Pulliam
NSF Division of Human
Resource
DevelopmentLouis Stokes Alliance
for Minority
Participation program
(HRD-0703554)
NSF Division of
ChemistryCenters for Chemical
Innovation program
(CHE-0847919)