The a priori calculation of collisional energy transfer in highly vibrationally excited molecules: the biased random walk theory

An a priori calculation of collisional energy transfer has been carried out, based on an extension of Gilbert’s ‘‘biased random walk’’ model [J. Chem. Phys. 80, 5501 (1984)]. The model assumes that energy migration during the collision is random except for certain physical and statistical constraints. It is shown that the probability of energy transfer can be obtained accurately from a relatively small number (10–50) of trajectories using a Smoluchowski equation and generalized Langevin equation approach. Calculations for the azulene/argon system, employing realistic inter- and intramolecular potentials, show excellent agreement with the experimental results of Rossi, Pladziewicz, and Barker [J. Chem. Phys. 78, 6695 (1983)] and Hippler, Lindemann, and Troe [J. Chem. Phys. 83, 3906 (1985)]. This suggests that the extended model may be reliably and economically used to calculate appropriate energy transfer quantities. Moreover, a number of general trends seen in experimental results can be rationalized with the model.