Close-coupling and coupled states calculation of low energy He–CH4 and Ne–CH4 collisions

Exact close-coupling calculations are used to evaluate the effectiveness of the coupled states approximation in the interpretation of low energy, noble gas methane collisions. The effect of the higher order angle dependent terms of the potential on the inelastic rotational transition was investigated. Calculations using only open channel basis functions were clearly different from converged calculations, but the differences were small enough to be negligible in comparison with experiment. It was shown that open channel coupled states calculations are of sufficient accuracy to evaluate the agreement of the potential model with experiment. The use of the coupled states approximation does not fully account for discrepancies between theory and experiment observed earlier.