Diatomic Molecules

Abstract

Following the above discussion of some important realistic examples of catalysis, we turn to the theory of chemical bonds outside metal surfaces. In this chapter, we shall be concerned primarily with the effect of the proximity of a planar metal surface on the binding energy of a diatomic molecule. Of course, it is clear that when the charge clouds of metal and molecule overlap strongly, then significant perturbations of the molecular valence electrons can and do occur. However, even before the molecule enters the “spill-out” region of itinerant electrons from the metal, one may expect some influence of the metal on the bond strength and length. This is because there will be an additional interaction between the electrons in the molecule through the response of the metallic electrons to the charge fluctuations in the molecule. Though a full calculation of this effect is not an easy matter, it will be demonstrated below, for instance in a diatomic molecule parallel to the metal surface, that this additional interaction will tend to weaken the bond.