Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements VIII. Ar XIII with new features

Ar XIII is found to be unique with new features in electron-ion recombination not seen in any other ion. The ion has been studied with the unified method which provides a theoretically self-consistent set of atomic parameters for the inverse processes of photoionization and total electron-ion recombination. The unified method subsumes both the radiative recombination (RR) and dielectronic recombination (DR) within the framework of close-coupling formulations using the R-matrix method. A set of four DR "bumps", two in the low and two in the high temperature regions, is found to exist in the recombination rates of Ar XIV + e $\to$ Ar XIII. This is in contrast to two typical DR "bumps", one at high temperature common for most ions and one at low temperature depending on the presence of near threshold autoionizing resonances in the bound-free process. The large scale ab initio calculations for Ar XIII employ eigenfunction expansion of 37 core Ar XIV states from n = 2 and 3 complexes. This enables core excitations of type $\Delta n$ = 0 and 1. Ar XIII exhibits more extensive resonant structures and wider PEC (photoexitation-of-core) resonances for n = 3 core states than those of n = 2 states. Hence the high energy region of photoionization and recombination are dominated by these structures. Total and partial photoionization cross sections of all bound states, state-specific recombinaion rates of 561 bound states and total recombination rate coefficients are presented.