Direct and resonant photoionization of highly charged aluminum-like Ca7+ ions

Photoionization of Ca7+ ions from the ground [Ne]3s23p 2P1/2 and the excited [Ne]3s23p 2P3/2 and [Ne]3s3p2 4P1/2 states is investigated using the relativistic R-matrix theory. Regarding the ground-state photoionization, both direct and resonance ionization limits are determined, while the resonance peak structure of the Rydberg series is analyzed by searching for resonance positions. Furthermore, some resonance peaks are identified by matching the energy levels with resonance positions, which are attributed to the resonances [Ne]3s3lnl′ (l=p,d) at the level of (fine-structure) energy levels or configurations. As for the excited state, it is hardly possible to identify the resonance peaks and ionization limits owing to their dense distribution and complexities of resonance structure, even though the direct photoionization limits are determined. It is expected that the present analysis on the photoionization of Ca7+ ions could be used for diagnostics and modeling of calcium plasmas, along with photoionization data of other calcium ions.