Application of interpolating moving least squares fitting to hypervelocity collision dynamics: O(3P) + HCl.

We use an automated interpolating moving least-squares (IMLS) algorithm, which generates a fitted ab initio surface for systems of arbitrary topology, to construct a global OHCl ((3)A'') surface at the UB3LYP/aug-cc-pVTZ level of theory. This analytic PES includes all reaction channels and OHCl geometries with energies up to 144 kcal/mol (6.25 eV) above the O + HCl asymptote. The fitted surface was combined with the quasiclassical trajectory method to study the dynamics of the O((3)P) + HCl reaction at hyperthermal collision energies. The fitted PES greatly improves energy conservation during trajectory integration and eliminates problems with ab initio convergence, which are often encountered during direct dynamics studies. The more extensive trajectory calculations yield new insight into the title reaction and agree well with previous experimental studies and direct dynamics results.