Jason J. Pajski, Matt Logan, Brian C. Dian1, Gordon G. Brown, Kevin O. Douglass, Richard D. Suenram and Brooks H. Pate

Department of Chemistry, University of Virginia, McCormick Rd., P.O. Box 400319, Charlottesville, VA 22904

1.) Department of Chemistry, Purdue University, 560 Oval Dr., West Lafayette, IN 47907

David F. Plusquellic

Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899

BROADBAND ROTATIONAL SPECTRA OF THE SOMAN-RELATED

COMPOUNDS: PINACOLYL ALCOHOL AND PINACOLONE

11 GHz CP-FTMW Spectrometer

Pulse Monitor

12 GHz Oscilloscope (40 Gs/s)

Free Induction Decay

0.5 – 11.5 GHz

Arbitrary Waveform Generator Chirped Pulse

Frequency Sweep

4 GS/sx8

7.5 - 18.5 GHz

TWTAmplifier

FID acquisition and Fourier transform

9.9 GHz PDRO

2 GHz Bandwidth

Nozzle Sample Feed

18.99 GHz PDRO

Chemical Warfare Agent Simulants

• Pinacolone

• Pinacolyl Alcohol

Soman (GD) – nerve agent (cholinesterase inhibitor)

Pinacolyl Alcohol

Pinacolyl Alcohol Constants

1Calculated with MP2/6-311++G(d,p)

Experimental Calculated1 Δ (obs-calc)

A (MHz) 3085.1061 3095 -9.894

B (MHz) 2226.0068 2251 -24.99

C (MHz) 1858.6123 1874 -15.39

ΔJ (kHz) 1.01×10-3

ΔJK (kHz) 1.21×10-4

ΔK (kHz) -5.64×10-4

δJ (kHz) 2.93×10-4

δK (kHz) -4.09×10-3

PinacoloneA-E splitting

Pinacolone - MP2/cc-pVTZPinacolone - MP2/cc-pVTZ

Rotational constants (MHz):A=3211 B=2334C=1936

Dipole moment (Debye):μa = -1.1 μb = 2.3 μc = 0.0Tot= 2.6

Rotational constants (MHz):A = 3218 B = 2322C = 1935

Top-of-barrier - Planar – ERel = 151.55 cm-1

Equilibrium - Non-Planar – ERel = 0.0 cm-1

Dipole moment (Debye):μa = -1.1μb = 2.4μc = 0.0Tot= 2.6

Rotational constants (MHz):A = 3213 B = 2326C = 1932

Equilibrium - Planar – ERel = 149.68 cm-1

Dipole moment (Debye):μa = -1.1 μb = 2.4μc = 0.0Tot= 2.6

13C Isotopomers

RelativeIntensity

1-13C 1.16 %

3-13C 1.22 %

4-13C 1.14 %

8-13C 1.01 %

12-13C + 16-13C 2.84 %

Unassigned Line

Qualitative Quantum Mechanical Argument

Pinacolone Constants

Experimental vs. CalculatedParameters for Pinacolone

Experimental1 Calculated2 Δ (obs-calc)

A (MHz) 3192.091(2) 3211 -18.909

B (MHz) 2292.898(2) 2334 -41.102

C (MHz) 1928.181(2) 1936 -7.819

Barrier to rotation (cm-1)

122.3(5) 109.39 12.91

1Values are for the A-state.2Calculated at MP2/cc-pVTZ level.

Conclusions for Pinacolone

• A-E splittings from methyl rotor

• Experimental barrier determined to be 122.3(5) cm-1

• Pinacolone is dynamically planar

• Some molecules cool only to next-lowest energy state in a double well with a probability density centered off the c-axis giving rise to extra lines in the spectrum

Acknowledgements

Pate Lab Group Members

Rick Suenram and David Plusquellic at NIST

Funding:• NSF Chemistry

• SELIM Program

• NSF MRI Program (with Tom Gallagher, UVa Physics)

• University of Virginia

• John D. and Catherine T. Macarthur Foundation

• The Jeffress Trust

Approximate Energy Gap for c-Type Transitions with the Double Well Assumption

ΔE ~ 2-4 cm-1 ~ 60-120 GHz

Pinacolone - MP2/6-311++G(d,p)

Rotational constants (MHz): 13C Isotopomers

C1 3187 2306 1917C3 3188 2310 1919C4 3167 2281 1891C8 3155 2294 1898C12 3145 2283 1913C16 3143 2294 1905

Chirped Pulse Generation: x8 Scheme

x4 x2

7.5 – 18.5 GHz

To Experiment

Chirped Pulse Frequency

Sweep 162.5 – 1537.5 MHz

Phase locked oscillator 9.9

GHz

10 MHz Rb Oscillator

4 GHz Arb. Waveform Generator

Dual Channel Independent

Trigger

Laser/TWT Trigger

Scope Trigger

0-80 dB Programmable

Atten.

Single Sideband Filter

Sweep 9.7375 –

8.3625 GHz

Sweep 19.15 –

13.65 GHz

19.8 GHz

High Power TWT Amplifier

x2

Low Power Loop

2nd Generation Chirped Pulse Design

7.5 – 18.5 GHz

To Experiment

Chirped Pulse Frequency

Phase locked oscillator 13.0

GHz

10 MHz Rb Oscillator

Arbitrary Waveform Generator

Dual Channel Independent

Trigger

Laser/TWT Trigger

Scope Trigger

High Power TWT Amplifier

Chirped Pulse (Linear Frequency Sweep) Excitation

))((0

0)( ttieEtE

2

0

2)(

))((

tt

ttdt

d

Chirped Pulse

Instantaneous Frequency:

pulset

t

0

= sweep rate

Need: 11,000 GHz/1s

Synthesizer: 300MHz/1ms

Use arbitrary waveform

generator as the frequency source

Need sweep rates that are 105

times faster than standard synthesizers

11 GHz Chirped Pulse

Frequency Sweep in Time Frequency Sweep in Frequency

Signal recorded at -60 dB from 1kW TWT

Pinacolyl Alcohol - MP2/6-311++G(d,p)

Principal axis orientation: --------------------------------------------------------------------- Center Atomic Coordinates (Angstroms) Number Number X Y Z --------------------------------------------------------------------- 1 6 -0.650404 0.032244 0.004389 2 6 -1.350092 -1.214783 -0.552939 3 1 -2.412953 -1.199323 -0.286090 4 1 -1.274510 -1.243391 -1.646845 5 1 -0.901567 -2.127883 -0.154701 6 6 -0.753548 0.029199 1.533699 7 1 -0.350085 0.949614 1.968617 8 1 -1.805919 -0.042861 1.831211 9 1 -0.214816 -0.822931 1.957450 10 6 -1.344202 1.278396 -0.558481 11 1 -1.222157 1.341073 -1.646826 12 1 -2.417517 1.232254 -0.343728 13 1 -0.956358 2.199782 -0.112868 14 6 0.817475 0.008628 -0.459379 15 1 0.802567 -0.009424 -1.561871 16 6 1.663694 1.191937 -0.001797 17 1 1.719657 1.228696 1.089120 18 1 2.684030 1.088694 -0.389624 19 1 1.267264 2.139412 -0.375790 20 8 1.387245 -1.216911 0.018817 21 1 2.320061 -1.204391 -0.215811 --------------------------------------------------------------------- Rotational constants (MHZ): 3095.1951021 2250.9551932 1873.5365802

Pinacolone - MP2/6-311++G(d,p) Principal axis orientation: --------------------------------------------------------------------- Center Atomic Coordinates (Angstroms) Number Number X Y Z --------------------------------------------------------------------- 1 6 0.884204 -0.173084 -0.015204 2 8 1.365019 -1.296014 -0.022361 3 6 -0.632438 0.046343 -0.006184 4 6 1.782644 1.051913 -0.006567 5 1 1.407179 1.834645 0.657137 6 1 2.787990 0.753317 0.293749 7 1 1.824740 1.468676 -1.018755 8 6 -1.342606 -1.254925 -0.381769 9 1 -2.426918 -1.100734 -0.361246 10 1 -1.055174 -1.580544 -1.386322 11 1 -1.086291 -2.057253 0.314085 12 6 -1.036003 0.455622 1.422104 13 1 -0.568880 1.398108 1.725585 14 1 -2.122703 0.588764 1.468339 15 1 -0.755514 -0.320547 2.142141 16 6 -1.022012 1.157367 -0.991699 17 1 -0.702012 0.911595 -2.010664 18 1 -2.111652 1.270494 -0.999520 19 1 -0.587370 2.122896 -0.715873 --------------------------------------------------------------------- Rotational constants (MHZ): 3187.9664865 2314.6458259 1922.0286113