Introduction

The physics of chemisorption hinges on the static and dynamic properties of the surface chemical bond. Bond formation, bond stability and bond dissolution all are crucial to our subject. In this chapter we begin our investigation motivated by the well-known intimate connection between bonding and structure (see, e.g., O'Keeffe & Navrotsky (1981)). The spatial distribution, strength and reactivity of the electronic bonds within a chemisorption complex depend sensitively on the relative position of the adsorbate and substrate nuclei. In the best case, all bond distances and bond angles will be known to any desired numerical accuracy. Minimally, we should know the local symmetry of the adsorption site, the gross orientation of the adsorbate with respect to the surface and the nature of any structure within the adsorption layer itself. Unfortunately, in the world of surface science, none of these quantities reveals itself in a straightforward, mechanical fashion.

What is the geometrical arrangement of atoms in the surface region of a clean crystal after adsorption by a foreign species? Consider first the case of a single adatom. As discussed in Chapter 8 for the case of Au/NaCl(100), the most probable binding sites occur at substrate positions where the total adatom/substrate potential energy of interaction has minima.