MOLECULAR-INTERACTIONS ON SURFACES

The potential energy surfaces describing interactions between molecules lie at the heart of much chemical physics. Numerous spectroscopic and scattering techniques can provide a fairly direct measure of the interactions between gaseous species. Less detailed information is available for the lateral interactions between adsorbed molecules since these must be inferred from their impact upon static, kinetic, and dynamic surface phenomena. We have recently combined measurements of the coverage-dependent isothermal molecular desorption rate and adsorption isotherms with a quasiequilibrium analysis to make progress in understanding the general features of the lateral interaction potential between similar and different adsorbed molecules. Results from a variety of systems ranging from physisorption to weak chemisorption are presented which emphasize several dominant trends. Our results for physisorption systems are generally quantitatively consistent with a lateral potential described by a simple screened gas phase potential. For chemisorption systems, however, we often find evidence for a weak attractive well in the lateral potential with no counterpart in the gas phase potential. These weak attractions have a pronounced impact upon coverage-dependent static and kinetic phenomena.