Absolute cross sections for electron-impact single ionization of Kr4+, Kr5+, and Kr7+ ions

Absolute total cross sections for electron-impact single ionization of Kr4+, Kr5+, and Kr7+ ions have been measured using a crossed-beams technique from below threshold to 500, 400, and 500 eV, respectively, with absolute uncertainties of 12% or less. The measured cross sections are in good agreement with distorted-wave calculations and show significant contributions from excitation autoionization. Nonzero cross sections below threshold for the Kr4+ and Kr5+ ions suggest the presence of metastable ions in those two species that were extracted from an electron-cyclotron-resonance ion source. Such evidence of metastable ions was not found in the case of the Kr7+ ion measurment.