Adsorbate-assisted adsorption: trapping dynamics of xenon on platinum(111) at nonzero coverages. Arumainayagam, Christopher R.; Stinnett, James A.; McMaster, Mark C.; Madix, Robert J. Dep. Chem., Stanford Univ., Stanford, CA, USA. J. Chem. Phys. (1991), 95(7), 5437-43. CODEN: JCPSA6 ISSN: 0021-9606. Journal written in English. CAN 115:215748 AN 1991:615748 CAPLUS (Copyright 2001 ACS)

The trapping dynamics of Xe on Pt(1110 was probed as a function of Xe coverage with supersonic mol.-beam techniques. Adsorption probabilities were measured directly at a surface temp. of 95 K at coverages ranging from zero to monolayer satn. at incident translational energies between 6 and 63 kJ/mol and incident angles between 0 and 60°. In apparent agreement with the predictions of the original P. Kisliuk (1957) model, the adsorption probability at the lowest incident translational energy (6 kJ/mol) remains almost const. with coverage up to near monolayer satn. However, in contradiction to the original Kisliuk model, at higher incident translational energies, the trapping probability increases nearly linearly with Xe coverage up to near monolayer coverage. For example, the trapping probability increases from 0.06 to 0.42 for an incident translational energy of 63 kJ/mol at normal incidence as the coverage is increased from zero to satn. monolayer coverage. This behavior can be explained adequately by a model that incorporates enhanced trapping onto the monolayer compared to the clean surface, a property of the model that is confirmed directly by expts. presented herein. The angular dependence of the adsorption probability shows progressive deviation from normal energy scaling with increasing Xe surface coverage, proving that the degree to which parallel momentum participates in the adsorption process increases with adsorbate coverage. The initial trapping probability of Xe onto the monolayer is independent of incident angle indicating total-energy scaling. The above findings are qual. identical to the authors' previous results for the mol. adsorption of ethane on the same surface, suggesting that these phenomena occur, in general, for weak mol. adsorption regardless of mol. shape and internal degrees of freedom, at least for small mols.