The Effect of Vibronic Coupling on Methyl Conformation in p-Cresol

Author Institution: Dept. of Chemistry, Montana State UniversityThe jet cooled fluorescence excitation spectrum of $S_{1}$ p-cresol shows that the methyl group does not change conformation upon excitation for totally symmetric modes but does for vibronically coupled modes appearing at 709, 1150 and $1529 cm^{-1}$ above the origin. We speculate that the second electronic state mixed in by the vibronic coupling causes an asymmetry in the electron density with respect to the para axis of the molecule thereby changing the hyperconjugation interaction and affecting the methyl conformation. This result helps confirm the possibility of using methyl groups as a probe of excited state electronic density and character. An assignment of the vibrational structure will be given