			15min:

ROTOR-VIBRATOR COUPLING EFFECTS IN METHYL CH STRETCHING OVERTONE SPECTRA OF GASEOUS TOLUENE.

D. CAVAGNAT, L. LESPADE AND C. LAPOUGE, LPCM, Université Bordeaux I, F-33405 Talence Cedex.

The methyl CH stretching overtone spectra of toluene and of its deuterated derivatives (C₆D₅CH₃, C₆D₅CH₂D and C₆D₅CHD₂) have been recorded by FTIR ( Delta v=1 to 4) and by intracavity dye laser photoacoustic spectrometry ( Delta v=5 and 6) at low resolution (0.5 to 2 cm^-1).

The different couplings likely to affect these spectra (anharmonic coupling of the CH mode with the methyl group internal rotation, Fermi resonance coupling with combination states involving CH stretch/methyl bending modes) are considered. The parameters used to model these couplings are determined partly from ab-initio calculations, partly from fitting simultaneously the spectra of the different isotopic compounds.

A preliminary analysis of the obtained results is presented. An attempt to compare them with those determined from the study of the corresponding overtone spectra of nitromethane (which presents a similar hindering barrier to the methyl group rotation) is made in order to check the effect of the molecular environment of the methyl group on IVR phenomena.