STATE-TO-STATE COLLISIONAL VIBRATIONAL-ENERGY TRANSFER IN S1 P-DIFLUOROBENZENE

State-to-state vibrational energy transfer from six levels in S1 p-difluorobenzene (pDFB) vapor at 300 K has been studied for single collisions with argon atoms. The levels range in vibrational energy up to 818 cm-1 and involve quanta of nu5, nu6, nu8, and nu30. This investigation is a continuation of a previous study concerning the zero-point level. The study is based on a laser pump-dispersed fluorescence detection method that monitors all significant one-collision channels from a given initial state. In common with results from other studies of polyatomic vibrational energy transfer, large state-to-state rate constants (up to 0.2 times hard sphere) are observed with high selectivity among possible final states. Among the 30 modes of pDFB, processes with small quantum changes in the two lowest-frequency modes, nu8 and nu30, dominate the energy transfer. Transfer to nearly resonant levels is generally too inefficient to observe. The rate constants for gaining or losing quanta of nu8 and of nu30 are insensitive to the vibrational identity of the initial state. The collisional flow patterns from each level are semiquantitatively described by a previously developed treatment of the SSH-T vibrational energy-transfer model.