ROLE OF SURFACE THERMAL MOTION IN THE DISSOCIATIVE CHEMISORPTION AND RECOMBINATIVE DESORPTION OF D-2 ON AG(111)

Although D-2 dissociation exhibits a large barrier on Ag(111), recombi native desorption occurs with minimal translational energy release. A strong surface temperature dependence is seen with a bimodal energy re lease at high temperatures. We propose that desorption occurs through two channels: by recombination at thermally activated sites, with a hi gh steric constraint but low activation barrier, and directly via a la rge barrier at high surface temperatures. Surface thermal motion deter mines the distribution of dissociation barriers, a model which will be important in other activated systems.