Contributions of resonant excitation double autoionization to the electron-impact ionization ofFe15+

Electron-impact ionization cross sections for ${\mathrm{Fe}}^{15+}$ have been calculated using relativitsic distorted-wave methods. We have performed the most comprehensive calculation to date by including more than 10 000 autoionizing levels for resonant-excitation double-autoionization (REDA) processes. The total cross sections exhibit many strong narrow resonances. The REDA process contributes about 30% to the average total cross sections. General good agreement between theory and experiment is attained, but new experimental investigations are needed to search for the predicted resonances.