Surface Science 167 (1986) 297-312 297 North-Holland, Amsterdam THE EFFECT OF ADSORBATE-ADSORBATE INTERACTIONS ON STIMULATED DESORPTION YIELDS * E B STECHEL and M L KNOTEK Sandta Nattonal Laboratories, Albuquerque, Neu Me~tco 87185, US4 Received 14 June 1985, accepted for pubhcatlon 30 October 1985 A treatment is g~ven of the effect of lateral interactions between adsorbed species on the desorptton 2¢leld from surfaces In a number of well-studied systems, e g H/W(100), Mo(100) CO/NI W, and O/W(100), Mo(100) it is observed that after an initial hnear increase of electron stimulated ~on desorptlon yield at very low coverage, a region of negatl~ e differential ton yield with increasing coverage Is encountered The yield achieves a maximum and then decreases with further coverage as the coverage exceeds a quarter to a half monolayer depending upon the system Here we present model calculations based on the hypothesis that this decreasing yield IS due to lateral delocahzatmn of the desorpt~on causing excitation as the interaction between adsorbed species increases A specific apphcatJon is the H/W(100) system where we find that a simple model indicates that such delocallzatlon could cause a decrease in the desorptlon yield m excess of one order of magmtude in going from a quarter monolayer to a half monolayer coverage Several experimental tests of thts model are suggested I. Introduction Some of the primary physical effects which govern stimulated desorptton yields from surfaces have begun to be isolated However, while it has long been appreciated that the yield is strongly dependent on the nature of the chemical state of the adsorbate, thts reahzat~on has only recently been put mto the form of models which are capable of describing those properties of a bond which govern the stimulated desorpt~on process The chemical configuration of the desorbmg species determines whether energy can be deposited m a way that desorpt~on ~s a viable avenue for releasing the stored electromc energy Of equal ~mportance ~s the couphng of the species to its environment which determanes the hfetlme of the state reducing desorpt~on In the model of Menzel, Gomer and Redhead (MGR) [1-3] this hfetlme parameter is for- mulated in terms of an escape probabd~ty P, so that the cross section for the desorptaon process is of the form o ~ %P where o¢ ~s the electronic cross * This work performed at Sandla National Laboratories supported by the US Dept of Energy under contract No DE-AC04-76DP00789 0039-6028/86/$03 50 © Elsevier Science Pubhshers B V (North-Holland Physics Pubhshmg Division)