Following excitation ofthe V3 mode in matrix isolated CH 3 F, population of 2V3 is observed. Population of2v3 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 X 10-35 and 6.7 X 10 -35 cm 6 S-I in Xe at 10 and 20 K, respectively. These probabilities were obtained from fluence dependent studies of the rise rate of 2V3 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 CH3F when excited via V3 vs excitation at 3000 cm -I is also rationalized. The temperature dependence and fluence dependence of deactivation rates of V3 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.

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The vibrational relaxation time for pure SiH4 is 0.10, 0.083 and 0.072 ^sec atm (±30%) at 295 K, 375 K and 462 K. For SiH4 diluted in He, D2 and H2 the corresponding numbers are 0.16, 0.081 and 0.031 /usee atm ( + 30%) at 295 K. The binary two-level theory has been used to determine the four V -R, T rates in the system SiH4 -CH4, and the rate for V-V exchange between SiH4 and CH4 from experimental data. From the Schwartz-Slawsky-Herzfeld-formula for V -T and V -V, T processes an equation is derived describing V -R and V -V, R energy exchange. The different models are compared with experimental data, especially with those found for the system SiH4 -CH4.

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