Electron-impact excitation autoionization of Ga II

The general-reaction theory of Feshbach is applied, within the framework of the distorted-wave approximation, to the calculation of excitation-autoionization resonances in the electron-impact ionization of ${\mathrm{Ga}}^{+}$. Although the spectrum of autoionizing levels for ${\mathrm{Ga}}^{+}$ is quite complex, we focus our attention on the important $3d^{10}4s^2\to 3d^{9}4s^{2}4p$ inner-shell excitations. For excitation of the $3d^{9}4s^{2}4p {}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ autoionizing level we make a general-reaction-theory calculation for the dominant partial-wave cross section and compute a typical resonance profile in the ejected-electron differential cross section. We find that the quantum-mechanical interference between the direct and indirect processes has a small effect on the total ionization cross section. Employing an independent-processes approximation we calculate excitation-autoionization contributions to all twelve levels of the $3d^{9}4s^{2}4p$ configuration. Using the results of our calculations and their comparison with a recent crossed-beam experiment by Rogers et al., we discuss the accuracy of the distorted-wave method and the effects of configuration interaction on energy levels and excitation cross sections.