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CLASSICAL DYNAMICS OF LOCAL CH-STRETCHINGS OF AN ALMOST FREELY ROTATING METHYL GROUP

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Title: CLASSICAL DYNAMICS OF LOCAL CH-STRETCHINGS OF AN ALMOST FREELY ROTATING METHYL GROUP
Creators: Abbate, S.; Montagnoli, Enrico; Longhi, G.
Issue Date: 1998
Abstract: Cavagnat and Lespade have extensively examined the CH-stretching fundamental and overtone spectra of molecules containing an almost freely rotating $CHD_{2}$-group: Nitromethane. Toluene, etc. They were able to interprete the spectroscopic features by a model based on the assumption of moderate variations of the rotational potential with the stretching quantum number. Their approach was also tried on the same or similar molecules containing undeuterated methyl $groups.^{(1,2)}$ We have examined a classical model for almost freely rotating $CH_{3}$ and $CHD_{2}$-groups, allowing for just kinetic coupling between the CH-stretching and the methyl hindered rotation, with three different values for the rotation barrier applicable to the cases presented in refs. (1) and (2). While for $CHD_{2}$ just two types of classical regular trajectories are found at all overtone orders, namely those exhibiting either a torsion or a rotation in the methyl, for $CH_{3}$ a third type of trajectories appears at high overtone order, showing a 1:6 (or 1:12) resonance between the CH-stretching and the hindered rotation frequencies and a secondary 1:1 (or 1:2) resonance which is particularly evident in the momenta. The consequences of this fact in the semiclassical quantization scheme for the construction of the spectra will be discussed.
URI: http://hdl.handle.net/1811/18940
Other Identifiers: 1998-RG-10
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