A quasiclassical trajectory study of H+H₂O→OH+H₂: Angular distributions and OH angular momentum alignment

We present a detailed theoretical study of the H+H₂O reaction dynamics using quasiclassical trajectories and two potential energy surfaces, one from Walch-Dunning-Schatz-Elgersma (WDSE) and one from Isaacson (I5). Collision energies of 1.0, 1.4, and 2.2 eV are considered, and both scalar and vector properties of the product distributions are presented. The vector properties include polarization-dependent differential cross sections (PDDCS) and angular momentum alignment parameters for both OH and H₂. The WDSE and I5 scalar and vector results are in most respects very similar. However, we find that they differ noticeably with respect to angular momentum alignment, with I5 predicting weak OH alignment, while WDSE shows much stronger alignment with the OH angular momentum vector preferentially perpendicular to the scattering plane. The I5 surface is a more recent and more accurate surface for H₃O, so it is extremely encouraging that the alignment predicted by I5 is in quantitative agreement with a recent measurement from Brouard and co-workers. In addition, the I5 differential cross section matches the Brouard results quantitatively, while WDSE does not. Detailed mechanistic information underlying the angular distributions, alignment, and PDDCS results is presented, and we find that the differences between I5 and WDSE alignments are connected to different energy release characteristics of the surface in the corner cutting region.