Studies of a model of hydrogen recombination

Abstract

A Morse oscillator model for recombination of hydrogen and its isotopes was investigated computationally. The model is very similar to one recently studied by Pritchard and co-workers. The aims of the study were the test of certain approximations and the determination of the range of validity of the model. It was found that at low temperatures the steady state approximation is an increasingly accurate and increasingly convenient approximation. A way of estimating the error arising from this approximation was proposed. Other approximations which were tested gave unsatisfactory results. The rate constant vs. temperature curve for the model does not agree well with the experimental curve for hydrogen in argon except insofar as it reproduces the observed levelling-off at high temperatures. For the model this result may be ascribed to increasing relative rates for multiquantum transitions among the levels of the diatom. The model does give the experimentally observed ratios of the rate constants for H- and D-atom recombination. This result indicates that the important factor in determining the isotope ratio is the effect of mass change on the density of states rather than its effect on the collision dynamics.