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

Abstract

Charge stripping of keV He2+, 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 He22+, 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 X2 Sigma u+ state of He2+ to the X1 Sigma g+ state.