Negative ion resonance of a molecule adsorbed on a metal surface covered with a rare gas monolayer

The characteristics of negative ion states formed by temporary electron attachment to adsorbed molecules depend on the environment of the molecule. Adsorption site effects on the energy positions and widths of the N2-2Πg resonance are theoretically investigated for a nitrogen molecule adsorbed on an Ar monolayer covering a Cu metal substrate. The molecule is shown to preferentially adsorb above the valleys between Ar atoms, with its axis parallel to the Ar plane. The N2- characteristics are determined by a scattering approach with a 3D microscopic description of the adsorbed Ar layer. The anisotropy of the potential around the molecular adsorption site lifts the resonance degeneracy. For both resonance components, the energy is lowered and the lifetime is increased by the interaction with the Ar layer. The importance of the effect of the Ar-vacuum interface reflectivity observed in an earlier study using a dielectric continuous medium description of the Ar layer is confirmed. Different adsorption sites and orientations are studied, revealing an adsorption site dependence of the resonance characteristics.