SUBSTRATE-MEDIATED DISPERSION INTERACTION EFFECTS IN THE PROPERTIES OF A PHYSISORBED GAS

The theory of substrate-mediated dispersion interactions is applied to analyze a set of quasiequilibrium measurements of adsorption isobars and desorption isotherms of the CH4/Ag(011) physisorption system. The theory provides for the construction of an adsorbate intermolecular po tential from the gas phase potential, with the spacing between the met al surface and the adsorbed layer as the sole adjustable parameter. Th e best fits to the kinetic and thermodynamic data yield a consistent i ntermolecular potential, with a well depth of approximately two-thirds of the free space value. The limited dynamic range of the measurement s does not permit a determination of the form of the intermolecular po tential. However, the good agreement of the theory with both data sets lends strong support for the quasiequilibrium model, and supports the proposition that the properties of physisorbed layers can be predicte d using gas phase potentials while accounting for substrate-mediated d ispersion interaction effects.