Plasmon mediated, long range, oscillating van der Waals forces between molecules adsorbed on metals

We use qualitataive arguments to propose a propensity rule stating that the van der Waals forces between adsorbed molecules may be strongly influenced by the surface plasmon. As a result, if the molecule has a narrow level resonant with a weakly damped surface plasmon, the van der Waals forces oscillate as a function of their separation and have an unusually long range.