Classical mechanics of recombination via the resonance complex mechanism: H + H + M → H2 + M for M = H, H2, He, and Ar

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Abstract
Rate constants for the recombination reaction H + H + M→H2 + M are calculated within the framework of the resonance complex theory for a variety of third bodies (M=H, He, Ar, and H2). The stabilization cross sections for bimolecular collisions of M with the highly excited orbiting resonance states of H2 were computed from exact three‐dimensional classical trajectories. Calculations were carried out for several different reasonable potential surfaces in order to determine the effects of variations in the interaction potential upon the macroscopic rate constant. For example, the inclusion of long range attractive forces between the inert third body and each H atom in H2 leads to a systematic increase in the low temperature rate constant. Using a best estimate for the potential parameters, good agreement with experiment is found for all the third bodies investigated over the temperature range ∼77–300°K. For inert third bodies it is shown that the so‐called ``energy transfer'' mechanism is much more important than the ``chaperon'' mechanism. However, for the case M=H, both mechanisms play a significant role with the ``chaperon'' mechanism being the more important. Furthermore, H atoms are found to be more efficient than inert M in causing recombination to occur. Data for the nonequilibrium ortho/para product distribution are also presented.