Vibrational energy transfer and migration processes in matrix isolated CH₃F

Following excitation of the ν₃ mode in matrix isolated CH₃F, population of 2ν3 is observed. Population of 2ν₃ occurs via intermolecular vibration-vibration (V-V) energy transfer driven by the exothermicity of the anharmonic V-V step equilibrating these states. In the equilibration process, both resonant and nonresonant intermolecular energy transfer processes have been identified. The probabilities of each of these processes have been determined. The phonon assisted nonresonant V-V process has a probability of 3.8×10^-35 and 6.7×10^-35 cm⁶ s^-1 in Xe at 10 and 20 K, respectively. These probabilities were obtained from fluence dependent studies of the rise rate of 2ν3 in concentrated matrices. V-V transfer has also been studied in dilute matrices and matrices of intermediate dilution. Signals obtained in these concentration regimes are not exponential but can be reproduced by a Monte Carlo model of V-V transfer. In these matrices there is no longer rapid vibrational energy migration on the time scale of vibrational deactivation. The consequences of the lack of rapid V-V transfer on this time scale are discussed. The difference in energy transfer behavior of CH ₃F when excited via ν₃ vs excitation at 3000 cm ^-1 is also rationalized. The temperature dependence and fluence dependence of deactivation rates of ν₃ excited CH₃F are also reported in Ar, Kr, and Xe matrices. By overcoating Ar and Kr matrices with Xe, the temperature range of these measurements has been extended beyond that previously reported.