First observation of He22+: charge stripping of He2+using a double-focusing mass spectrometer

Charge stripping of keV He 2 + , induced by collision with a neutral target gas in the field-free region of a mass spectrometer, is used to search for bound electronic states of He 2 2+ , including the ground electronic state. The use of a second energy analyser on the mass spectrometer and isotopic labelling were necessary to eliminate two severe interference processes which obscure the charge stripping process. When such precautions are taken a weak signal is observed which the authors have assigned to the transition from the X 2 Sigma u + state of He 2 + to the X 1 Sigma g + state.