A hot-atom reaction kinetic model for H abstraction from solid surfaces

Measurements of the abstraction reaction kinetics in the interaction of gaseous H atoms with D adsorbed on metal and semiconductor surfaces, H(g) + D(ad)/S--> products, have shown that the kinetics of the HD products are at variance with the expectations drawn from the operation of Eley-Rideal mechanisms. Furthermore, in addition to HD product molecules, D, products were observed which are not expected in an Eley-Rideal scenario. Products and kinetics of abstraction reactions on Ni(100), Pt(lll), and Cu(lll) surfaces were recently explained by a random-walk model based solely on the operation of hot-atom mechanistic steps. Based on the same reaction scenario, the present work provides numerical solutions of the appropriate kinetic equations in the limit of the steady-state approximation for hot-atom species. It is shown that the HD and D, product kinetics derived from global kinetic rate constants are the same as those obtained from local probabilities in the random walk model. The rate constants of the hot-atom kinetics provide a background for the interpretation of measured data, which was missing up to now. Assuming that reconstruction affects the competition between hot-atom sticking and hot-atom reaction, the application of the present model at D abstraction from Cu(100) surfaces reproduces the essential characteristics of the experimentally determined kinetics. (C) 2000 Elsevier Science B.V. All rights reserved.