david wilcox purdue university department of chemistry 560 oval dr. west lafayette, in 47907-2084
TRANSCRIPT
66th Ohio State University International Symposium on
Molecular Spectroscopy 6/23/2011
The Microwave Spectrum of Methyl Vinyl Ketone Revisited
David Wilcox
Purdue University
Department of Chemistry 560 Oval Dr.
West Lafayette, IN 47907-2084
Methyl Vinyl Ketone (MVK) in Atmospheric Chemistry
•Product of isoprene oxidation
•Correlated with biogenic isoprene*
•Generates destructive carbonyls that contributes to ozone destruction**
Methyl Vinyl Ketone
*D. Pierotti, S.C. Wofsy, D. Jacob, J. Geophys. Res. 95 (1990) 1871.
**E.C. Tuazon, R. Atkinson, Int. J. Chem. Kinet. 21 (1989) 1141.
Evidence for an Additional Conformer
•Infrared data: enthalpy +2.36 kJ/mol (Bowles et al.)
•Ab initio calculations
•Discharge spectrum of isoprene (unpublished results)
Previous Microwave Studies of MVK
•Foster et al. (7 to 33 GHz)
•Fantoni et al. (26.4 to 40 GHz)
•P.D. Foster, V.M. Rao, R.F. Curl, Jr., J. Chem. Phys. 43 (1965) 1064.•A.C. Fantoni, W. Caminati, R. Meyer, Chem. Phys. Lett. 133 (1987) 27.•A.J. Bowles, W.O. George, W.F. Maddams, J. Chem. Soc. B (1969) 810.
12 GHz Oscilloscope
(40 Gs/s)
200W
ArbitraryWaveformGenerator
100 MHz Quartz
Oscillator
GHz Chirped Pulse1.875-4.625 GHz
Pulsed Nozzle
0.4-11.4 GHz
1)
2)
3)
Free InductiveDecay
18.9 GHz PDRO
x47.5-
18.5 GHz
CP-FTMW Spectrometer
20 μs FID ~20 kHz resolution, interpolated to 5 kHz
MVK Microwave Spectrum
~100,000 time domain averages S/N 10,000:1
Internal Rotation Analysis I: Principal Axis Frame in JB95
A-state effective Hamiltonian:
E-state effective Hamiltonian:
with
Reduced barrier parameter (FR fixed to 5.3 cm-1)
R. Lavrich, D. Plusquellic, R. Suenram, G. Fraser, A. Walker, M. Tubergen, J. Chem. Phys. 118 (2003) 1253.
Propagation of error from cross-terms
(FR fixed to 5.3 cm-1)
• P.D. Foster, V.M. Rao, R.F. Curl, Jr., J. Chem. Phys. 43 (1965) 1064.• A.C. Fantoni, W. Caminati, R. Meyer, Chem. Phys. Lett. 133 (1987) 27.
*Includes transitions from refs:
*
Internal Rotation Analysis II: Combined-Axis Frame in XIAM
H. Hartwig, H. Dreizler, Z. Naturforsch 51a (1996) 923.
Rotational Hamiltonian in principal axis frame
Torsional Hamiltonian in Rho-axis frame
-Eliminates 2/3 torsion-rotation cross terms.
• P.D. Foster, V.M. Rao, R.F. Curl, Jr., J. Chem. Phys. 43 (1965) 1064.• A.C. Fantoni, W. Caminati, R. Meyer, Chem. Phys. Lett. 133 (1987) 27.
*Includes transitions from refs:
*
fixed
Comparison with Ab Initio Calculations
HF* DFT** JB95 XIAM A (MHz) 9056.92 8912.33 8941.552(1) 8941.547(1) B(MHz) 4311.38 4258.51 4274.4144(4) 4274.3593(9) C(MHz) 2974.36 2936.50 2945.3365(5) 2945.2903(9)V3 (cm-1) 397.5 258.7 433(4) 433.8(1)θa (o) 80.72 81.63 78.5(7) 78.21(2)
ap-MVK
HF* DFT** JB95 XIAM A (MHz) 10481.39 10229.70 10238.657(4) 10238.610(1)B(MHz) 4012.61 3979.18 3991.507(9) 3991.6814(6)C(MHz) 2954.22 2916.42 2925.652(1) 2925.4885(1)V3 (cm-1) 375.2 290.3 375(5) 376.6(2)θa (o) 32.78 32.71 36(5) 29.71(3)
sp-MVK
*6-311++G(d,p)**B3LYP/ 6-311++G(d,p)
Comparison of ap-MVK V3 with Previous Studies
• P.D. Foster, V.M. Rao, R.F. Curl, Jr., J. Chem. Phys. 43 (1965) 1064.• A.C. Fantoni, W. Caminati, R. Meyer, Chem. Phys. Lett. 133 (1987) 27.
I. Foster et al.
•V3 = 437(7) cm-1
Fixed parameter: FR = 5.33 cm-1
II. Fantoni et al.
•V3 = 424(7) cm-1
Fixed parameter: F = 5.38 cm-1
This study
•V3 = 433.8(1) cm-1 (XIAM) = 433(4) cm-1 (JB95)
Fixed parameter: FR = 5.30 cm-1
Structure of sp-MVK
1.504(9) Å
1.475(9) Å
1.333(7) Å
C3 C4
C1
C2
C1
C2 C3 C4a
b
Principal Axis Orientation: C2,C4
•C2: 0.06 Å from a-axis
•C4: 0.1 Å from a-axis
Structure of ap-MVK
C1
C2 C3 C4
ab
Principal Axis Orientation: C2,C41.48(2) Å
1.492(8) Å 1.340(6) Å
C3 C4
C1
C2
1.24(1) Å
•C2: 0.06 Å from a-axis
•C4: 0.08 Å from a-axis
Summary of Results•CP-FTMW spectrometer: sp-MVK unambiguously detected with high S/N
•V3 barrier precision and experimental resolution: JB95 and XIAM
•Efficient structural analysis with CP-FTMW spectrometer •Revisit spectra of related molecules
OSU Molecular Symposium 6/23/2011
Acknowledgments
Funding:
Purdue University
Camille and Henry Dreyfus Foundation
Co-authors:
Amanda ShirarOwen WilliamsBrian Dian
Special Thanks:
David PlusquellicIsabelle Kleiner
Appendix : Rotational Parameters for MVK Isotopologues
Identification of Isotopologues in Natural Abundance
A) Improved accuracy for isotopic rotational constant predictions:
I) Calculatedus– Experimentalus = Δus
II) Calculateds – Δus →
Predictions within 100 kHz to 1 MHz of experimentally determined rotational constants
B) Isotope νA- νE splitting consistent with unsubstituted splitting.
C) 13C identified in both ap- and sp-MVK 18O lines for the A-state of ap-MVK.
Notes on Kraitchman Analysis
•Approximate rigid rotor constants in the absence of internal rotation
•18O A-states within 10% of the rigid rotor constants.
J. Demaison, L. Margulès, I. Kleiner, A. Császár, J. Mol. Spec. 259 (2010) 70.