SUPERSONIC JET FLUORESCENCE-SPECTRA OF 4-METHYLSTYRENE - GROUND-STATE VIBRATION WAVE-NUMBERS AND IMPROVED TORSIONAL POTENTIAL FUNCTIONS

Single vibronic level (dispersed) fluorescence spectra of 4-methylstyrene, with excitation in various excited vibrational levels of S1, have provided wavenumbers of some a′ and a″ vibrations in S0 and energy levels for the C(1)-C(α) vinyl torsional and the methyl torsional vibrations. The estimated values of the parameters for the torsional potentials are V″2= 943±58 cm-1, V″4= -208±31 cm-1, for vinyl torsion in S0; V″3= 28±4 cm-1, V″6= -7±1 cm-1, for methyl torsion in S0; and V″3= -8±4 cm-1, V″6= -19±4 cm-1, for methyl torsion in S1. The vinyl group is coplanar with the benzene ring in S0. The methyl group is eclipsed, relative to the benzene ring, in S0, but almost staggered in S1. © 1992.