Combined effect of relaxation and channel interaction on outer-shell photoionization in Ar,K+, andCa2+

Abstract

The influence of relaxation and final-state channel interaction on 3p and 3s photoionization of Ar, ${\mathrm{K}}^{+}$, and ${\mathrm{Ca}}^{2+}$ has been studied by multiconfiguration multichannel Dirac-Fock method. The total relaxation effect was separated into reduction of the ionization energy and into an energy-dependent modification of the photoionization cross section. For 3p subshell the relaxation reduced the cross section at their maxima, near threshold, by 10–20 % and vanished about 100–140 eV above threshold. The relaxation decreased the Ar 3s cross section whereas the ${\mathrm{Ca}}^{2+}$ 3s cross section is enhanced slightly even at large photon energies. The relaxation effect decreases rather slowly with the increasing ionic charge. Our results indicate that the relaxation is nonadditive and of comparable importance with other leading many-electron effects. This emphasizes the necessity of a unified treatment of static and dynamic correlation effects.