Excitation-autoionization through 3d-4linner-shell excitations in Cu- to Kr-like ions and the effect on fractional-ion-abundance balance in coronal plasmas

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Abstract
Excitation of inner-shell electrons into autoionizing levels followed by autoionization (EA) can enhance the total ionization rate. For ions isoelectronic to elements of the fourth row, the present results show that the enhancements can be much more important than those previously calculated for the preceding isoelectronic sequences. Δn=1 3d-4l inner-shell excitations, which are the dominant EA channels, are considered here. Detailed computations of EA rates were performed using the relativistic distorted-wave method, and the behavior of the EA rate coefficients along the Cu, Zn, Ga, and Kr isoelectronic sequences has been analyzed. In the other sequences from Ge to Br with configurations involving a very large number of levels, EA calculations have been performed for a few elements only. In view of an easy use of the data, and for application to other elements, approximate analytical expressions have been deduced for ionization energies, average inner-shell excited-configuration energies, total electron-impact excitation rates, as well as average branching ratios for autoionization. These data enable a direct evaluation of the EA rates in all the sequences from Cu to Kr for all the elements with 40≤Z≤92. Finally, the EA rate coefficients were introduced in the coronal ionization rate equations. Fractional ion abundances for Mo (Z=42), Xe (Z=54), Pr (Z=59), and Dy (Z=66) obtained with and without taking into account EA processes are presented. The results show a decrease of up to 40% in the temperature of maximum abundance for Kr- to Ni-like ions.