Physical approach to theH2↔ H+H reaction: Friction coefficient calculation

A study of the dynamical aspects related to the ${\mathrm{H}}_2$ ↔ H+H reaction on a metal surface is presented. Starting from a model Hamiltonian formulation the binding energy between the two adatoms and the friction coefficient $\eta$, both for relative and center-of-mass motion, are calculated. $\eta$, which is related to the prefactor in the Arrhenius reaction rate equation, shows variation over a wide range of values as a function of separation between the adatoms. At the same time $\eta$ exhibits a markedly different behavior depending on whether the adatoms are in a magnetic or nonmagnetic configuration. The implications of our results for recent work on catalysis are briefly discussed.