Measurements of cross sections for inner- and outer-shell ionization of Rb+, Cs+, Ca+and Sr+ions by electron impact

Cross sections have been measured for the ionization of Rb + , Cs + , Ca + and Sr + ions by electron impact. In the cases of Rb + and Cs + the shapes of the ionization functions displayed irregularities which were attributed to the direct ejection of inner-shell electrons. By contrast, the ionization functions of Ca + and Sr + exhibited very large and abrupt rises centred at 27 and 26 eV, respectively. These were attributed to the onset of autoionization which, for a wide range of electron energies, was the dominant mode of ionization. An interpretation of the measurements is presented which is based on the results of recent calculations by Hansen (1974).