Chemisorption on metals

The field of chemisorption has recently seen great advances both in experimental spectroscopies for examining the geometry and electronic structures of adsorbed species and in numerical calculational techniques. The aim of this article is a critical analysis of these results, especially theoretical ones, with emphasis on the relationship to simple models of chemisorption. An important conclusion is the strong coupling nature of many chemisorption systems, i.e. that there exists something like a chemical bond between the adsorbate and the nearest-neighbour substrate atoms with their associated bonding and antibonding electronic levels.We start by outlining the phenomenological fundamentals, such as the structure of the adsorbed layer. Basic theoretical concepts, such as local density functional theory, on which much of the modern discussion of the electronic chemisorption problem depends, and the electronic structure of the clean surface, are then outlined. There follows a fuller discussion of the Anderson model, which is regarded as the underlying canonical model for considering chemisorption. A discussion, in detail, of the theoretical and some experimental aspects of a number of systems is then given. The principal systems considered, which are of contemporary interest, include hydrogen, oxygen and alkalis on free-electron and transition metals, chalcogenides on nickel, CO adsorption on various transition metals, and oxygen on silver.