Photoionization with excitation and double photoionization of the helium isoelectronic sequence

We perform a systematic study of photoionization with excitation and double photoionization of H^-, He, and 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 O⁶⁺, accurate nonrelativistic results for photoionization with excitation to arbitrarily high n and double photoionization may be obtained for all heliumlike targets.