High-temperature vibrational-rotational relaxation in He-H₂

The vibrational-rotational relaxation of He-H₂ at high temperatures is studied by applying a recently developed exponential distorted wave (EDW) technique to calculate inelastic cross sections. Particular attention is given to the role of the high rotational states in vibrational relaxation; transfer through these states is shown to be important at high temperatures. For conditions simulating He-H₂ shock tube experiments, a single exponential decay is found to describe the n=0→n′→1 vibrational relaxation for all time. It is shown that this fortunate circumstance, which is important in the interpretation of such experiments, does not necessarily extend to other widely differing experimental conditions.