ELECTRON-IMPACT DOUBLE-IONIZATION OF CA+ IONS

The absolute cross section for the double ionization of Ca+ from thres hold to 500 eV has been measured for the first time. A combination of electron beam modulation and fast energy-scanning techniques was used. At energies around 340 eV the cross section displays several steps an d resonant peaks, which can be identified as arising from autoionizati on processes involving the excitation of a 2p electron. There is littl e evidence of structure elsewhere in the cross section,although some p oints of inflexion are apparent in the region below 90 eV.