Electron-impact single ionization of krypton ions (q= 12-18)

Absolute cross sections for electron-impact single ionization of krypton ions Kr q + ( q = 12-18) have been measured. The animated crossed-beam method has been applied. The measurements cover the energy range from threshold to about 5.5 keV. The presence of ions formed in metastable states is observed for Kr 18+ , Kr 16+ and Kr 14+ . Inner-shell excitation from the 2s, 2p, 3s and 3p subshells followed by autoionization is seen to play a dominant role for this reaction over the whole energy range. The importance of these excitation-autoionization processes explains the large underestimation of cross sections from the available theoretical and semi-empirical estimations which include direct processes only.