Relativistic Effects in Atomic and Ionic Photoionization: “Anomalous” Behavior at the Low End of Isoelectronic Sequences

The relativistic resonances between the 2 p 3/2 and 2 p 1/2 thresholds of the first three members of the Ne isoelectronic sequence are shown to evolve in a highly complex manner along the sequence. The phenomenon is explained, and its generality over the entire periodic table is established. These results show that the coupling scheme required for accurate calculations can change dramatically from species to species along a sequence. This can have important implications for calculations of near-threshold photoionization and low-energy electron-ion recombination rates of astrophysical importance.