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

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•Discharge spectrum of isoprene (unpublished results)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.