Excitation autoionization rates from ground and excited levels in Li-likeAr15+to S-likeAr2+

Abstract

The rate coefficients for excitation autoionization (EA) from the levels of the ground and first excited configuration in nearly all argon ions (Li-like Ar${}^{15+}$ to S-like Ar${}^{2+})$ have been computed. Collisional excitation cross sections are computed in the distorted-wave approximation and integrated over a Maxwellian distribution of free-electron energies. Radiative and autoionizing transition probabilities are computed using the fully relativistic, intermediate coupling code RELAC. For each ion, the rates of EA are compared to semi-empirical calculations of the direct ionization rate. For charge states with few $M$-shell electrons in the ground configuration (Na-, Mg-, and Al-like), EA can significantly enhance the direct ionization rate coefficients. In the first excited configuration of each ion considered, the EA rate coefficient enhances the direct ionization rate coefficient only at low temperatures.