EXCITATION-FUNCTION FOR H- A STUDY OF ZERO-POINT ENERGY EFFECTS AND ROTATIONAL DISTRIBUTIONS IN TRAJECTORY CALCULATIONS(O2 REACTION )

The excitation function of the H + O2 (nu = 0) --> OH + O reaction has been determined from trajectory calculations using the HO2 DMBE IV po tential energy surface. Reactive cross sections for thirteen translati onal energies, corresponding to a total of a quarter of a million traj ectories, have been computed covering the range 65 less-than-or-equal- to E(tr)/kJ mol-1 less-than-or-equal-to 550. Various schemes for analy zing the trajectories, three of which aim to correct approximately for the zero-point energy problem of classical dynamics, have been invest igated. One of these schemes aims to correct also for known requiremen ts on rotational distributions, e.g., for the fact that by Hund's rule s for the coupling of angular momentum the product OH (2PI) molecule a lways rotates. It has been found that zero-point energy effects and lo west-J constraints on rotational distributions may have a crucial role , especially close to the threshold energy of reaction. Agreement with recent measurements of absolute reactive cross sections is generally satisfactory but, unlike experiment, no sharp maximum is found on the excitation function in the vicinity of E(tr) = 170 kJ mol-1. Possible reasons for this discrepancy are discussed. There is also good agreeme nt with existing experimental data on the products rotational distribu tion.