Contribution of excitation autoionization to the electron-impact ionization of Ar7+

Abstract

We report a detailed calculation of the contribution of excitation autoionization to the electron-impact ionization of Ar{sup 7+} by a distorted-wave Born approximation with exchange. Inner-shell excitations of the type 2{ital s}{sup 2}2{ital p}{sup 6}3{ital s}{r_arrow}2{ital s}{sup 2}2{ital p}{sup 5}3{ital snl} ({ital n}=3,4,5; {ital l}=0,1,2,3) and 2{ital s}{sup 2}2{ital p}{sup 6}3{ital s}{r_arrow}2{ital s}2{ital p}{sup 6}3{ital snl} ({ital n}=3,4; {ital l}=0,1,2,3) are included. The level-to-level excitation cross sections and autoionization branching ratios are calculated in detail. The present results demonstrate that the use of unit branching ratios will overestimate the excitation-autoionization cross section by about 20{endash}40{percent}. Furthermore, the calculation shows the largest contribution is from 2{ital p}{r_arrow}3{ital p} and 2{ital p}{r_arrow}3{ital d} excitations and the latter dominates the contribution of excitation autoionization to electron-impact ionization. The calculated results are also compared with recent experimental measurements and theoretical calculations. Being different from the results of Griffin, Bottcher, and Pindzola [Phys. Rev. A {bold 45}, 2929 (1992); {bold 24}, 2273 (1981)], our results for the branching ratio are closer to the measurement of Rachafi {ital et} {ital al}. [J. Phys. B {bold 24}, 1037 (1991)] and our values are smaller than the experimental one of Zhang {ital et} {ital al}. [Phys. Rev. Amore » {bold 45}, 2929 (1992)], while the results for the unit branching ratio are very close to the calculation of Tayal [Phys. Rev. A {bold 49}, 2561 (1994)]. In addition, we find that the configuration interaction changes the autoionization branching ratios of individual levels, but has little effect on the total excitation-autoionization cross sections. {copyright} {ital 1996 The American Physical Society.}« less