Electron-impact single ionization of multiply charged aluminium ions

Absolute total cross sections for electron-impact single ionization of Alq (q = 3-7) ions are investigated experimentally as well as theoretically. E mploying the crossed-beams technique, the cross sections have been measured from below the respective ground state threshold up to 1 keV and partly up to 5.5 keV. The theoretical calculations were performed using the configur ation-averaged distorted-wave method, including both direct ionization and excitation-autoionization contributions from the 2p-shell. The measurements are in good agreement with the calculations considering a small content of metastable ions in the incident ion beam. Because of the strong dominance by direct ionization processes the semiempirical Lotz formula can describe the measured data as well.