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.

404

505

303

202

212

313

414

515

413Linked Map

of

Quantum

States

Frequency Range Extension

Checking assignment of rotational

spectra of molecules which helps to

identify molecules.

Do

ub

le

Re

son

an

ce

Monitor- A-Type 16430 MHzScan- 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 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

Left Potential Well

X

Y

E

Right Potential Well

Y

X

E

Tunneling

E E

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

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

DR

Monitored

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.

Personal Thanks to:

Brooks Pate

Matt Muckle

Justin Neill

Amanda Steber

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)