ASSESSMENT OF THE ROLE OF QUANTAL EFFECTS IN THE DYNAMICS OF STIMULATED DESORPTION

We have assessed the roles of various quantum effects in the stimulate d desorption spectra and yields of isolated physisorbed species. By an appropriate extension of the semiclassical (Antoniewicz's) and strict ly quantum wave-packet squeezing (WPS) models of desorption with dissi pative coupling of the ionized adsorbate to the substrate electronic r esponse, we were able to describe quantum effects associated with elas tic and inelastic adsorbate motion within a unified model. Using this model we investigated the possibility of removing the long-standing di screpancies between large values of experimental desorption yields fro m adlayers of Ar atoms on Ru(001) and much smaller ones calculated in Antoniewicz's and WPS models by using empirical atom-surface potential parameters. The desorption rates thus calculated turned out to be rat her insensitive to dissipative effects due to a smooth transition betw een Antoniewicz's and WPS desorption regimes, which could be explained by the properties of the wave packets describing the ionized adpartic le motion. This indicated that the desorption rates would be sensitive only to the variations of the neutralization rate and parameters spec ifying neutral- and ionized-state diabatic potentials. By varying the latter we showed that high enough desorption yields could be reproduce d only with extreme forms of the ionized-state potentials. From this w e conclude that improved models of stimulated desorption need take int o account certain aspects of the many-body lateral adsorbate-adsorbate interactions.