Photoionization with excitation and double photoionization of the helium isoelectronic sequence

Abstract

We perform a systematic study of photoionization with excitation and double photoionization of ${\mathrm{H}}^{\ensuremath{-}},$ He, and ${\mathrm{Li}}^{+}$ using the convergent close-coupling formalism. The present calculations cover the photon energy range from the double-ionization threshold to 10 keV where the results go over continuously to the nonrelativistic limit of infinite photon energy. By consideration of scaling properties, tested by application to ${\mathrm{O}}^{6+},$ accurate nonrelativistic results for photoionization with excitation to arbitrarily high n and double photoionization may be obtained for all heliumlike targets.