THE ROLE OF STICKING AND REACTION PROBABILITIES IN HOT-ATOM MEDIATED ABSTRACTION REACTIONS OF D ON METAL-SURFACES BY GASEOUS H-ATOMS

Recent experiments on the abstraction of D adsorbed on metal surfaces with gaseous hydrogen atoms revealed a kinetics of HD formation which is not compatible with the operation of Eley-Rideal (ER) mechanisms. F urthermore, homonuclear products were observed during abstraction, whi ch are not expected through an ER reaction scheme. It was therefore su ggested that hot-atom (HA) mechanisms are more appropriate to explain the measured kinetics and products. Random walk calculations of the ab straction kinetics are presented based on a model which exclusively re lies on elementary reaction steps which are HA mediated processes. Wit hin this model, the ratio of two variables, the probabilities for hot- atom sticking at empty sites p(s) and hot-atom reaction with adsorbed species p(r), was found to control the kinetics of HD and D-2 formatio n. The essential features of measured kinetic data at Ni(100), Pt(lll) , and Cu(lll) surfaces were reproduced by simple and reasonable assump tions on p(s)/p(r). (C) 1998 American Institute of Physics. [S0021-960 6(98)70334-4].