Chemical bonds well outside metal surfaces

In a model of diatomic molecules in which the long-range part of the interatomic potential energy curve is due to the London non-retarded dispersion interaction between the constituent atoms, it is shown that the proximity of a metal surface weakens the strength of the chemical bond when the molecule is parallel to the metal surface. The theory is based on the nature of the dyadic Green function connecting the electric field with a dipole source outside the metal surface-this is established by use of image theory. For a Lennard-Jones-type interatomic potential it is shown that the maximum reduction of the bond strength in the parallel configuration is 4/9.