Effects of Variations of the Potential-Energy Surface on the Attributes of Simple Exchange Reactions: Classical Calculations

The results of numerically exact classical‐trajectory calculations for the collinear collision of $\mathrm{H}+{\mathrm{H}}_2$ on a series of Wall‐Porter potential‐energy surfaces are presented and compared with previously reported accurate quantum‐mechanical results. The effects of variations of (1) the total energy, (2) the barrier height, (3) the curvature of the reaction path, and (4) the slope and ``width'' of the potential barrier along the reaction path on various attributes of the reaction are determined by systematically changing selected parameters of the surface. Attributes of primary interest are (1) the reaction probability (as a function of energy), (2) the effective threshold for reaction, and (3) the degree of vibrational excitation of the product, as measured by the fraction of the total energy which ends up as vibrational energy of the product. It is observed that the classical results agree better with the quantum‐mechanical for some surfaces than for others. Also, although the detailed structure of the reaction probability curves is not well predicted in the classical approximation, the classical and quantum‐mechanical results agree on the ``average,'' indeed, incredibly well for some surfaces.