Electron-ion recombination rate coefficients and photoionization cross-sections for Al XI, Al XII, Si XII, Si XIII for UV and X-ray modeling

Results are presented from detailed study of inverse processes of photoionization and electron-ion recombination of (hν + Al XI ⇋ Al XII + e), (hν + Al XII ⇋ Al XIII + e), (hν + Si XII ⇋ Si XIII + e), and (hν + Si XIII ⇋ Si XIV + e) using ab initio unified method. These are the first results on photoionization cross-sections (σPI(nSLJ)) with autoionizing resonances and level-specific recombination rate coefficients, incorporating both the radiative and dielectronic recombination, for these ions. All fine structure levels with n ⩽ 10 and 0 ⩽ l ⩽ 9 are considered. A total of 98 fine structure levels with 1/2 ⩽ J ⩽ 17/2 for Al XI and Si XII, and 190 for Al XII and 189 for Si XIII with 0 ⩽ J ⩽ 10 are found. σPI(nSLJ) show background enhancements due to core excitations and narrow high-peak resonances. Level-specific recombination rates show smooth decay with a small bump at high temperature. Present total recombination rate coefficients with temperature (αR(T)) show good agreement with available rates. Recombination rates over photoelectron energy (αR(E)) are presented for astrophysical and laboratory plasma applications. Total recombination rates for H-like Al XIII and Si XIV are given for completeness. Calculations are carried out in the relativistic Breit-Pauli R-matrix method using coupled channel wavefunctions. Inclusion of important atomic effects such as radiation damping, channel couplings, interference of DR and RR, and relativistic fine structure effects should provide accuracy within 10–15%. The comprehensive datasets are applicable for various models such as for ionization balance and recombination-cascade for UV and X-ray lines.