Optical excitation spectra of rare-gas atoms physisorbed on metal surfaces

Abstract

Numerical computations are presented for the optical excitation spectra of neutral rare-gas atoms physisorbed on various metal surfaces. At low coverage and when the damping of the surface plasmons is much greater than the effective radiative damping, the occasional disappearance of the spectral lines of the optical absorption is due to a cancellation process, which occurs between the frequency profiles arising from two nearby excited states of the adsorbed atom. The red (blue) shifted peak of the symmetric mode of the higher (lower) excited state and the blue (red) shifted peak of the antisymmetric mode of the lower (higher) excited state of the atom cancel each other out provided that the frequency profiles of their lineshapes nearly coincide. Results of numerical calculations indicate that at low coverage the peaks of excited Xe on Ti and Au and excited Kr on Mg, in addition to those of Xe on Al and Kr on Au, vanish; this is compatible with the experimental observations. Predictions have been made for the adsorption spectra as a function of the distance from the atom to the surface of excited Xe and Kr, which are physisorbed on the surfaces of W, Ni, and Rh, respectively.