Role of indirect-ionization processes in the electron-impact ionization ofFe15+

We have investigated the contributions of excitation-autoionization and resonant-excitation-double-autoionization indirect-ionization processes to the electron-impact ionization of ${\mathrm{Fe}}^{15+}$ using a close-coupling approximation. The total ionization cross sections are obtained by adding the cross sections for these indirect processes to the direct-ionization cross sections. Eleven autoionizing levels arising from the 2$p^5$3$s^2$, 2$p^5$3s3p, 2$p^5$3$p^2$, and 2$p^5$3s3d configurations, together with the ground 2$p^6$3s state, are included in the close-coupling expansion. Large numbers of bound terms of appropriate symmetry are included in the expansion to account for the resonant-excitation-double-autoionization process. The present results are in good agreement with the recent crossed-beam measurement.