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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