RYDBERG STATES OF THE HYDROGEN-ATOM NEAR A METAL-SURFACE

We consider n = 20 Rydberg states of the hydrogen atom interacting wit h a nearby metal surface over an atom-surface distance range of 105 nm -530 nm. We show that the traditional quadratic approximation to the p otential is insufficient to follow the true potential and one needs to include higher order terms to obtain accurate energies for these Rydb erg states. We include terms up to eighth order in the electron-proton distance in the potential and demonstrate by means of basis set calcu lations that the resulting spectra differ significantly from those obt ained in the quadratic approximation. We observe an energy spread of t he n = 20 manifold which is roughly twice that given by the quadratic approximation. Observed level repulsions are attributed to z-parity sy mmetry breaking. We compare our results with those from degenerate per turbation theory.