Application of stochastic theory to vibration–rotation inelasticity in the He–H2 system

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Abstract
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 vibration–rotation inelasticity in the He4–(para‐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 Fokker–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 vibration–rotation states of H2 are energetically accessible. Very strong near‐resonant vibration–rotation inelasticity was found from the high rotational levels (j∼18). The results are compared to quantum mechanical calculations and experimental measurements.