DYNAMIC ROTATIONAL SPECTROSCOPY OF METHYL VINYL ETHER MEASURED

DYNAMIC ROTATIONAL SPECTROSCOPY OF METHYL VINYL ETHER MEASURED BY CHIRPED-PULSE FOURIER TRANSFORM MICROWAVE (CP-FTMW) SPECTROSCOPY Gordon G. Brown, Justin L. Neill, Steven T. Shipman, and Brooks H. Pate Department of Chemistry, University of Virginia, Mc. Cormick Rd. , P. O. Box 400319, Charlottesville, VA 22904 TF 05 Mini-Symposium Dynamics Probed by Spectroscopy Tues. 2: 56

Potential Energy Surface of Methyl Vinyl Ether (MVE) 110 -101 101 -000 202 -111 312 -303 211 -202 202 -101 B 3 LYP/6 -31+G(d, p) -CH 3 Torsio nal An gl e 101 -000 Barrier to methyl rotation: cis: 1157 cm-1 (1291 cm-1)1 gauche: 397 cm-1 (427 cm-1)2 Calc (Exptl) 1 Fujitake and Hayashi, J. Mol. Struct. 127, 21 (1985). Cupp, Lee, and Pate, J. Mol. Spectrosc. 193, 150 (1999). 2 Mc. Whorter, cis gauche 1448 cm-1 695 cm-1 2143 cm-1

Motivation for DRS of MVE • Ruoff, Kulp, and Mc. Donald observed conformational isomerization of MVE after IR laser excitation* • 2 large amplitude motions accessible at excitation energy (with high barrier for isomerization) – Increased complexity in DRS *Rodney S. Ruoff, Thomas J. Kulp, and J. D. Mc. Donald, J. Chem. Phys. 81, 4414 (1984).

Coalescence Phenomenon No Reaction Lifetime Broadening Frequency Pulling Coalescence Narrowing A A B kf kr B Increasing Reaction Rate

Gyroscope Dynamics C: Coalescence Parameter

MW-IR Double Resonance Spectroscopy of MVE • Measure conformer-specific rotationally resolved IR spectrum of each conformer of MVE – Cavity-FTMW – detected IR spectrometer • Measure Dynamic Rotational Spectra of vibrationally excited (C-H stretch fundamental) MVE – Chirped-Pulse FTMW spectrometer

Cavity-FTMW – Detected IR Spectrometer (Single Mode Locked) Nd: YAG Pumped OPO/OPA Laser ~ 10 m. J/Pulse 3 m ~ 0. 02 cm-1 bandwidth Pulsed Valve 2 GS/s AFG IR Multipass T. J. Balle and W. H. Flygare, Rev. Sci. Instrum. 52, 33 (1981). R. D. Suenram, J. U. Grabow, A. Zuban, and I. Leonov, Rev. Sci. Instrum. 70, 2127 (1999) MW IR MW

Cavity-FTMW-detected IR spectra Monitor cis 101 -000 11264. 83 MHz cis V=1, J=1 IR Scan Monitor gauche 202 -101 17415. 13 MHz gauche J. R. Durig and D. A. C. Compton, J. Chem. Phys. 69, 2028 (1978). V=0, J=1 MW Probe V=0, J=0

Standard Model of IVR W -C-H Bright State Dark States Molecular Eigenstates

FTMW-detected IR spectra P(1) cis gauche R(1) R(0) P(2) R(2) V=1, J=1 P(1) R(1) A-type IR R(0) 6 IR bands ~1. 72 cm-1 frequency splitting 19 ps IVR out of bright state IR Scan A-type IR 2 IR bands ~0. 05 cm-1 frequency splitting 670 ps IVR out of bright state Monitor cis 101 -000 11264. 83 MHz V=0, J=1 MW Probe V=0, J=0

FTMW-detected IR spectra Monitor cis 101 -000 11264. 83 MHz cis V=1, J=1 A/B type IR Monitor gauche IR Scan 202 -101 17415. 13 MHz gauche A/B type IR V=0, J=1 MW Probe V=0, J=0

IR - chirped pulse-FTMW Double Resonance (Single Mode Locked) Nd: YAG Pumped OPO/OPA Laser ~ 10 m. J/Pulse 3 m ~ 0. 02 cm-1 bandwidth Side View Top View MW Pulsed Horns Valve Narrow. Band MW Source IR Multipass Timing: 1) Valve Pulse 2) Laser excitation 3) Microwave measurement

Dynamic Rotational Spectra P(1) P(2) P(1) Symm. –CH 3 Stretch R(2) R(1) R(0) R(1) V=1, J=1 MW Probe V=1, J=0 IR Pump P(1) V=0, J=1 V=0, J=0

DRS of Phenylacetylene V=1, J=5 MW Probe V=1, J=4 MW Probe V=1, J=3 IR Pump R(3) ~3330 cm-1 V=0, J=3

Dynamic Rotational Spectra cis θ = 57. 1˚ Symm. –CH 3 Stretch gauche V=1, J=1 MW Probe V=1, J=0 IR Pump P(1) θ = 23. 4˚ V=0, J=1 V=0, J=0

Dynamic Rotational Spectra Asymm. -CH 3 Stretch Symm. –CH 3 stretch

Conclusions • We have measured the IR spectrum of both the cis and the gauche conformer of MVE from 2800 – 3150 cm-1 – τIVR = 19 – 670 ps – Perturbations measured are mode specific and conformer specific • We have measured the dynamic rotational spectrum of MVE at several IR frequencies. – Conformational Isomerization occurs at all frequencies pumped – Methyl rotation leads to frequency shifts towards the gyroscope limit

Acknowledgements Pate Lab Group Members Funding: • NSF Chemistry • NSF MRI Program (with Tom Gallagher, UVa Physics) • John D. and Catherine T. Macarthur Foundation • University of Virginia

E-Pentenyne DRS

Methylbutenyne Dynamic Rotational Spectrum IR Prepares J=0 Exclusively through P(1) Excitation J=1 -0

Dynamic Rotational Spectroscopy Energy Bath States In the normal-mode basis, each vibrational state gives rise to a single rotational transition at a characteristic frequency given by its rotational constant 101 -000 C-H Zeroth Order Bright State

Dynamic Rotational Spectroscopy Energy Bath States In the normal-mode basis, each vibrational state gives rise to a single rotational transition at a characteristic frequency given by its rotational constant 101 -000 Populate only 000 C-H Zeroth Order Bright State

Dynamic Rotational Spectroscopy Bath States Energy W Molecular Eigenstates In the molecular eigenstate basis, each quantum state gives rise to many rotational transitions. Populate only 000 W C-H Zeroth Order Bright State Dn 600 MHz

Cavity-FTMW-detected IR spectra Monitor cis 101 -000 11264. 83 MHz cis V=1, J=1 IR Scan Monitor trans 202 -101 17415. 13 MHz gauche V=0, J=1 MW Probe V=0, J=0

IR – CP-FTMW – MW Triple Resonance connected not connected Timing IR CP-MW Narrow- Detect band MW FID

CP-FTMW Spectrometer

CP-FTMW Spectrometer

FTMW-detected IR spectra A/B-type IR cis V=1, J=1 R(1) P(1) ~1. 45 cm-1 frequency splitting 23 ps IVR out of bright state A-type IR IR Scan R(0) ~0. 05 cm-1 frequency splitting 670 ps IVR out of bright state Monitor cis 101 -000 11264. 83 MHz V=0, J=1 MW Probe V=0, J=0

FTMW-detected IR spectra Monitor cis V=1, J=1 IR Scan Monitor gauche V=0, J=1 MW Probe V=0, J=0

Narrowband FTMW cavity Spectrometer 2 GS/s AFG Continuum MW Synthesizer Nd: YAG 10 Hz rep. rate ν 0 200 m. J/p 532 nm v 0 + 30 MHz Pulsed 1 watt amp Dye laser 0. 025 cm-1 Single Sideband ν 0 5 m. J/p UV bandwidth 5 Gs/s Oscilloscope (30 MHz Carrier) Free Induction Decay T. J. Balle and W. H. Flygare, Rev. Sci. Instrum. 52, 33 (1981). R. D. Suenram, J. U. Grabow, A. Zuban, and I. Leonov, Rev. Sci. Instrum. 70, 2127 (1999)

Dynamic Rotational Spectra V=1, J=1 MW Probe V=1, J=0 IR Pump P(1) V=0, J=1 V=0, J=0

Isomerization Rate of MVE τISOM = 47 ps τRRKM = 22 ps τISOM = 34 ps τRRKM = 18 ps