MOLECULAR-INTERACTIONS AND SIMPLE SURFACE PROCESSES

The potential energy surfaces that govern the interaction between similar or different molecules or atoms is a dominant theme in essentially all fields of condensed matter and gas phase chemistry and physics. They are relevant to diverse issues ranging from the geometries of van der Waals clusters to the structure of macromolecules. In principle, knowledge of the surfaces allows detailed modeling of atomic scale processes and thus of many structure-function relationships. Understanding the interactions between adsorbed molecules offers a particularly interesting challenge due to their inherent difficulty and to their practical importance. The many current efforts to simulate such processes are ultimately limited by our limited knowledge of how adsorbed molecules interact. One of the goals of this review is to discuss qualitatively some of these aspects of the problem of interacting adsorbed molecules. In principle, simple kinetic and thermodynamic measurements can provide useful information about these interactions. Establishing a qualitative and intuitive understanding of such measurements from the perspective of fundamental interactions provides an additional goal. We first discuss in general the factors affecting interactions between adsorbed molecules and how these are related to gas phase potentials. A simple and unified model to describe the impact of molecular interactions on simple surface phenomena, such as the desorption rate and adsorption isotherms that have developed over the past decade, is then reviewed. Finally, several applications of this procedure are reviewed and its limitations are discussed.