Previous papers considered describing molecular collisions by the techniques of nonequilibrium statistical mechanics. In the present work this stochastic theory of molecular collisions is applied to vibrationndash;rotation inelasticity in the He4ndash;(parahyphen;H2) system. Some improvement in the theory is presented to better handle energetic effects, particularly important in the weak coupling limit. The resulting formulation leads to the solution of simultaneous Fokkerndash;Planck and master equations for the rotational and vibrational motion, respectively. Scattering cross sections were computed for total energies from 1.3 to 4.0 eV. At this highest energy 85 vibrationndash;rotation states of H2are energetically accessible. Very strong nearhyphen;resonant vibrationndash;rotation inelasticity was found from the high rotational levels (jsim;18). The results are compared to quantum mechanical calculations and experimental measurements.
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