Applications of the relativistic equation of motion to photoionization of Mg-like ions

As an approximation to the relativistic equation of motion, the multiconfiguration relativistic random-phase approximation theory is applied to the valence-shell photoionization of the Mg-like ions. Photoionization cross sections between (2p63s)2S1/2(2p63s)2S1/2 and (2p63p)2P1/20 ionization thresholds are calculated. The main feature of our results is exhibited by five Rydberg series of doubly excited states arising from fine-structure splittings. A comparative study of Al+, Si2+, P3+, S4+, Cl5+, and Ar6+ is presented.