COVERAGE DEPENDENCE OF MOLECULAR ADSORPTION DYNAMICS - ETHANE ON PT(111)

The dynamics of associative adsorption of ethane on Pt(111) as a function of ethane coverage was probed with supersonic molecular beam techniques. Adsorption probabilities were directly measured at coverages ranging from zero to monolayer saturation at incident translational energies between 10 and 40 kJ/mol and incident angles between 0-degrees and 60-degrees at a surface temperature of 95 K. In contrast to the predictions of the original Kisliuk model, at all incident translational energies and incident angles the adsorption probabilities increases with ethane coverage up to near monolayer coverage. This behavior can be fit quite adequately by a model that incorporates enhanced adsorption onto the covered surface compared to the clean surface, utilizing the experimental value of the adsorption probability onto the saturated monolayer. The angular dependence of the adsorption probability shows progressive deviation from normal energy scaling with increasing surface coverage, suggesting that the effective corrugation of the gas-surface interaction potential increases with adsorbate coverage.