INTERNAL ROTATION-VIBRATION COUPLING CONTRIBUTIONS TO VIBRATIONAL LEVEL MIXING IN $S_{1}$ p-FLUORTOLUENE

$^{1}$ D.B. Moss, C.S. Parmenter and G.E. Ewing, J. Chem. Phys. 86, 51 (1987).Author Institution: Department of Chemistry, Indiana UniversityA comparison of two spectroscopically and structurally similar molecules, p-difluorobenzene (pDFB) and p-fluorotoluene (pFT), reveals the vibrational level mixing is greatly enchanced in pFT. Parmenter and Stone have suggested that this is due to the methyl rotor levels coupling to vibronic levels of the ring. Evidence for this coupling has been observed in dispersed fluorescence spectra of excited $S_{1}$ internal rotation levels in a cold molecular beam. The excitation of specific rotor states provides a test of a recently published$_{1}$ mechanism for this internal rotation-vibration coupling. A comparison of these results to selection rules for the mechanism will also be presented