Adsorption and desorption of O2 on Ag surfaces

A brief review of our measurements of the sticking probability of O-2 on Ag single crystal surfaces is presented. On Ag(110) and Ag(001) the non dissociative chemisorption probability behaves similarly increasing by three orders of magnitude as the oxygen translational energy is increased from 90 to 800 meV. The temperature dependence of the dissociative sticking probability allows to distinguish two different pathways to dissociation : on Ag(110) molecules can dissociate at terrace sites while on Ag(001) only special sites, tentatively identified with kinks, are effective. On Ag(111) the sticking probability is below the experimental sensivity. We finally report on the more recent results about the possibility to desorb or dissociate chemisorbed O-2 even at low temperature by collision with hyperthermal Xe atoms. (C) 1998 Elsevier Science Ltd. All rights reserved.