Variational transition state theory with leasthyphen;action tunneling calculations for the kinetic isotope effects in the Cl+H2reaction: Tests of extendedhyphen;LEPS, informationhyphen;theoretic, and diatomicshyphen;inhyphen;molecules potential energy surfaces

摘要

We apply conventional and variational transition state theory with leasthyphen;actionhyphen;groundhyphen;state and other transmission coefficients to calculate the rate constants and kinetic isotope effects for the reaction Cl+H2rarr;HCl+H. First we consider collinear reactions and compare the calculated results to accurate quantal results for a given potential energy surface. This tests the dynamical methods and shows that they are reliable enough for testing potential energy surfaces. We then make calculations for the threehyphen;dimensional reactions employing 11 potential energy surfaces that have been proposed in previous work. Seven of the surfaces are extended LEPS surfaces, as proposed by Persky, Klein, and Stern; Truhlar, Magnuson, and Garrett; and Valencich and cohyphen;workers; one is an informationhyphen;theoretichyphen;bondhyphen;orderhyphen;plushyphen;antihyphen;Morsehyphen;bend surface (called AL/AB) proposed by Agmon, Levine, Truhlar, Magnuson, and Garrett; and the final three surfaces are a diatomicshyphen;inhyphen;moleculeshyphen;plushyphen;threehyphen;centerhyphen;terms surface proposed by Baer and Last and two diatomicshyphen;inhyphen;molecules surfaces proposed by Isaacson and Muckerman. Three of the surfaces (the final surface of Persky, Klein, and Stern; the first surface of Truhlar, Magnuson, and Garrett; and the AL/AB surfacemdash;all of which have relatively symmetric saddle points) are shown to be more reasonable than the others for predicting the rate constants and the H2/D2and the HD/DH kinetic isotope effects. The calculations also indicate that the room temperature rate constants are dominated by quantum mechanical tunneling.