Electron impact ionization of O+, S+ and S2+ ions

Absolute cross sections for electron impact single ionization of O+, S+ and S2+ ions have been measured at an electron impact energy range from below threshold to 1000 eV, using the crossed beam technique. The measured cross sections for O+ ions are reproduced quite well with the semiempirical Lotz formula over the whole energy range investigated. The measured cross sections for S+ and S2+ ions show a more rapid rise from the threshold to their peak than those expected from the Lotz formula. For S2+ ions, another small bump beginning at 120 eV is observed, where no level exists that may contribute to any direct or indirect ionization processes. (author)