THEORETICAL AND SPECTROSCOPIC STUDY OF THE METHYL ROTOR DYNAMICS OF GASEOUS $-d_{0}, -d_{1}$ AND $-d_{2}$ NITROMETHANES IN HIGH EXCITED VIBRATIONAL STATES
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Date
1993
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Ohio State University
Abstract
The methyl CH stretching overtone spectra of gaseous $-d_{0}, -d_{1}$ and $-d_{2}$ nitromerthanes are reported from $\Delta \nu =1$ to 6. They display complex features with, for the $-d_{2}$ compound, a well defined rotation-vibration PQR structure which progressively disappears with increasing vibrational energy. From $\nu =5$, the spectra of the three isotopomers present three broad peaks with similar frequencies. A quantum $theory^{1}$, assuming an anharmonic coupling of the vCH mode with the internal rotation of the methyl group, combined with the results of recent ab-initio $calculations^{2}$, is used to analyse these experimental data. Theoretical calculations based on this model show that both methyl group internal rotation potential and methyl rotational structure contribute for the major part in determining the detailed features of the methyl CH stretching overtone region. The additional factors involving C-H stretch/bend and C-H/C-D stretch Fermi resonances are also considered. At high vibrational energy. the central band can be related to the average CH stretch during the methyl group rotation whereas the lower frequency peak can be assigned to the CH stretch of a C-H bond in a plane perpendicular to the molecular plane and the higher frequency one to the CH stretch of a C-H bond in the molecular plane.
Description
$^{1}$ D. Cavagnal and J. Lascombe, J. Mol. Spectrosc. 92. 141 (1982). $^{2}$ D. Gorse, D. Cavagnat. M. Pesquer and C. Lapouge, J. Phys. Chem. in press (1993).
Author Institution: Laboratoire de Spectroscopic Mol\'{e}culaire et Cristalline, URA 124, 351 cours de la Lib\'{e}ration, 33405; Laboratoire de Physicochimic Th\'{e}orique., URA 503. 351 cours de la Lib\'{e}ration
Author Institution: Laboratoire de Spectroscopic Mol\'{e}culaire et Cristalline, URA 124, 351 cours de la Lib\'{e}ration, 33405; Laboratoire de Physicochimic Th\'{e}orique., URA 503. 351 cours de la Lib\'{e}ration