DIRECT OBSERVATION OF INTERMOLECULAR ENERGY REDISTRIBUTION IN p-DIFLUOROBENZENE BY PICOSECOND GATING

Abstract

Author Institution: Department of Chemistry, University of Pennsylvania PhiladelphiaResults are presented on the picosecond time evolution of the fluorescence spectrum of p-difluorobenzene under collision free circumstances. Time-resolved single vibronic level emission spectra were obtained by the technique of frequency down-coversion by non-linear mixing of the molecular fluorescence with a picosecond laser pulse in a non-linear gating crystal. High resolution down-coverted spectra were obtained by using a monochromator and photo-multiplier tube; lower resolution down-converted spectra were obtained by using a spectrograph and a reticon array-based optical multichannel analyzer system. The time gated spectra consisted of structured emission corresponding to vibronic transitions superimposed on a diffuse background. The diffuse background displayed a time evolution that differed from that of the structured region of the spectrum. The observed kinetics might mean that intramolecular rovibrational energy redistribution is occuring on a timescale of ca. 6 ps