Exact and Approximate Quantum Mechanical Reaction Probabilities and Rate Constants for the Collinear H plus; H2Reaction

摘要

We present numerical quantum mechanical scattering calculations for the collinear Hplus;H2reaction on a realistic potential energy surface with an 0.424 eV (9.8 kcal) potential energy barrier. The reaction probabilities and rate constants are believed to be accurate to within 2percnt; or better. The calculations are used to test the approximate theories of chemical dynamics. The reaction probabilities for ground vibrational state reagents agree well with the vibrationally adiabatic theory for energies below the lowest threshold for vibrational excitation, except when the reaction probability is less than about 0.1. For these low reaction probabilities no simple onehyphen;mathematical dimensional theory gives accurate results. These low reaction probabilities occur at low energy and are important for thermal reactions at low temperatures. Thus, transition state theory is very inaccurate at these low temperatures. However, it is accurate within 40percnt; in the higher temperature range 450ndash;1250deg;K. The reaction probabilities for hot atom collisions of ground vibrational state reagents with translational energies in the range 0.58 to 0.95 eV agree qualitatively with the predictions of the statistical phase space theory. For vibrationally excited reagents the vibrational adiabatic theory is not accurate as for ground vibrational state reagents. The lowest translational energy of vibrationally excited reagents above which statistical behavior manifests itself is less than 1.0 eV.