A quasiclassical trajectory study of product energy and angular distributions in OH + H₂ (D2)

We present a quasiclassical trajectory study of OH + H₂ → H₂O + H and its D₂ counterpart using the Schatz-Elgersma semiempirical potential surface. Emphasis in the work has been on using an accurate determination of the H₂O vibrational actions to calculate product vibrational state distributions. Other aspects of the product energy and angular distributions have also been studied so as to make comparisons with recent molecular beam and laser experiments and with other calculations. The OH + H₂ results generally confirm earlier calculations by Schatz and Elgersma, but the vibrational distributions are somewhat different, indicating that the earlier perturbation theory-based calculations were not completely converged. The calculated OH + H₂(D₂) integral cross sections are in good agreement at energies close to the reactive threshold with quantum calculations due to Nyman and Clary. Comparisons with recent measurements by Koppe et al. indicate good agreement for OH + D₂ but not as good for OH + H₂. The OH + D₂ product angular distributions are in good agreement with measurements by Casavecchia and co-workers, but the fraction of energy in translation is significantly higher (0.45 vs 0.32). Nyman and Clary's fraction of energy in translation for the same potential energy surface is higher still (0.71). Their calculation leaves out HOD rotation, which may explain the differences between the two theoretical estimates. The difference between theory and experiment is probably due to inaccurate energy release behavior in the potential surface, with too little energy going to product vibration.