Theoretical Studies of Hot-Atom Reactions. II. Yields for Exchange Reactions of Hot Tritium Atoms with Hydrogen and Deuterium Molecules: Simple Models for Nonreactive Scattering

Abstract

Results of calculations of hot-atom yields and isotope effects for T atoms in H2 and D2 are reported for a variety of compositions. Use is made of the integral reaction probability formalism, quasiclassical reaction cross sections, and three simplified models for nonreactive scattering which preserve the energy independence of the average logarithmic energy loss. Theoretically predicted isotope effects are in good agreement with both high-energy T-recoil and low-energy photodissociation experiments for unmoderated systems. Anisotropic nonreactive scattering models give theoretical results generally in better agreement with experiment than does an isotropic model. The detailed energy and composition dependence of the hot-atom yield is examined and the errors incurred in the use of hot-atom kinetic theory are quantitatively analyzed. The kinetic-theory prediction that the high-moderator isotope effect is given by the ratio of the reactivity integrals and that the value is independent of the moderating mechanism is verified by results of the general theory for both 4He- and Ar-moderated systems. Explanation of discrepancies between the theoretical and experimental isotope effects in the high-energy limit for Ar-moderated systems appears to require calculations which make fuller use of the general integral reaction probability formalism.