Photoionization of H-and He above the n=2 threshold

Abstract

The photoionization cross sections of H^- and He(1¹S₀) have been calculated for incident photon energies above the n=2 threshold using Hylleraas bound state wavefunctions and close-coupling final state wavefunctions. At low energies it is found that excitation to the 2p state of the residual atom or ion is more probable than excitation to the 2s state, a result which is in disagreement with calculations which do not include the effects of close-coupling between the final states. An analysis indicates that the relative distribution between the n=2 states is determined mainly by the long-range 2s-2p dipole coupling. This is revealed by the dominance of a particular partial cross section in a representation which diagonalizes the long range r^-2 interactions coupling the degenerate n=2 states. Finally, the angular distribution of the ejected electrons is calculated in the case of H^-.