CONTRIBUTION OF EXCITATION AUTOIONIZATION TO THE ELECTRON-IMPACT IONIZATION OF AR7+

We report a detailed calculation of the contribution of excitation aut oionization to the electron-impact ionization of Ar7+ by a distorted-w ave Born approximation with exchange. Inner-shell excitations of the t ype 2s(2)2p(6)3s-->2s(2)2p(5)3snl (n=3,4,5; l=0,1,2,3) and 2s(2)2p(6)3 s-->2s2p(6)3snl (n=3,4; l=0,1,2,3) are included. The level-to-level ex citation cross sections and autoionization branching ratios are calcul ated in detail. The present results demonstrate that the use of unit b ranching ratios will overestimate the excitation-autoionization cross section by about 20-40 %. Furthermore, the calculation shows the lar e st contribution is from 2p-->3p and 2p-->3d excitations and the latter dominates the contribution of excitation autoionization to electron-i mpact ionization. The calculated results are also compared with recent experimental measurements and theoretical calculations. Being differe nt from the results of Griffin, Bottcher, and Pindzola [Phys. Rev. A 4 5, 2929 (1992); 24, 2273 (1981)], our results for the branching ratio are closer to the measurement of Rachafi er al. [J. Phys. B 24, 1037 ( 1991)] and our values are smaller than the experimental one of Zhang e r al. [Phys. Rev. A 45, 2929 (1992)], while the results for the unit b ranching ratio are very close to the calculation of Tayal [Phys. Rev. A 49, 2561 (1994)]. In addition, we find that the configuration intera ction changes the autoionization branching ratios of individual levels , but has little effect on the total excitation-autoionization cross s ections.