Influence of excitations to high-nlshells for the ionization process in theW26+ion

Abstract

It is shown that excitations from the ground configuration to high-$nl$ shells of the ${\text{W}}^{26+}$ ion have a large contribution to the electron-impact ionization process. Large-scale calculations for the excitations to over 900 configurations are performed using the Dirac-Fock-Slater approximation. The investigation includes subconfiguration-average and detailed level-to-level approaches. Our findings illustrate how important it is to study convergence of cross sections for the excitations to the high-$nl$ shells. The obtained results show that the excitations from the $4s$, $4p$, and $4d$ shells to the shells with the orbital quantum number $l=4$ dominate in the indirect process of the ionization. The excitation-autoionization cross sections make about 40% of the total ionization cross sections. Comparison between our data and previous configuration-average distorted-wave calculations for Maxwellian rate coefficients reveals large discrepancies for the direct and indirect parts of the ionization process.