Photoionization of Ar XVI and Ar XVII

Photoionization of Li-like argon, (hν+ArXVI→ArXVII+e), and He-like argon, (hν+ArXVII→ArXVIII+e), are studied using the relativistic Breit-Pauli R-matrix (BPRM) method. Results include both the partial and total photoionization cross-sections of fine structure levels with 1/2≤J≤17/2, n≤10 and 0≤l≤9 of Ar XVI and with 0≤J≤10, n≤10 and 0≤l≤9 of Ar XVII. They correspond to 98 bound levels of Ar XVI and 191 of Ar XVII. The close coupling wave function expansion for Ar XVI included 17 core levels up to n=3 thresholds and that of Ar XVII 16 core levels up to n=4 thresholds. Because of high-lying core excitations of these ions, the photoionization cross-section, σPI(nSLJ), decreases monotonically without features until at high energies where narrow high-peak resonances of Rydberg series of autoionizing states belonging to excited n=2 thresholds begin to appear. The dominant photoexcitation-of-core (PEC) or Seaton resonances also appear in the excited level cross-sections. The background of the total cross-section shows enhancement at n=2 thresholds due to resonant 1s-2p core excitations. However, the resonances become much weaker beyond n=2 thresholds. Radiation damping of resonances, important for these highly charged He- and Li-like ions, is included. These cross-sections are much improved over the existing TOPbase cross-sections where resonances, and background enhancements for Ar XVII were not included. With consideration of these effects, the present results should be accurate up to 10%-30% for various applications in modeling, recombination rates, opacities and diagnostic spectral analysis in the ultraviolet and X-ray regions. Cross-sections for H-like Ar are also included for completeness.

► Li- and He-like ions give important diagnostics for astrophysical and fusion plasmas. ► Ar XVI and Ar XVII photoionization show resonances giving various diagnostics lines. ► The resonances will increase the photoionization and recombination rates and opacities. ► Results correspond to first detailed cross-sections of many levels of these two ions. ► Photoionization of many excited levels will provide more complete astrophysical model.