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

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.