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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

David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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Page 1: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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

Page 2: 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.

Page 3: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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•Discharge spectrum of isoprene (unpublished results)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.

Page 4: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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

Page 5: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

MVK Microwave Spectrum

~100,000 time domain averages S/N 10,000:1

Page 6: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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.

Page 7: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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:

*

Page 8: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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.

Page 9: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

• 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

Page 10: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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)

Page 11: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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

Page 12: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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

Page 13: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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

Page 14: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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

Page 15: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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

Page 16: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

Appendix : Rotational Parameters for MVK Isotopologues

Page 17: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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.

Page 18: David Wilcox Purdue University Department of Chemistry 560 Oval Dr. West Lafayette, IN 47907-2084

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.