ELECTRON-CAPTURE IN COLLISIONS OF 5-67KEV AMU(-1) HE2-ATOMS( IONS WITH OXYGEN)

A crossed beam technique incorporating time-of-flight analysis and coi ncidence counting of the collision products has been used to study Oand O2+ formation in both one- and two-electron capture by 5.3-66.7 ke V amu(-1) He2+ ions in collisions with ground-state oxygen atoms. In t he case of one-electron capture, cross sections for simple charge tran sfer, which are known to be dominated by the He+(n = 2) + O+ S-4 produ ct channel at low energies, are found to attain a large peak value of about 1.8 x 10(-15) cm(2) at about 20 keV amu(-1). The low-energy tren d of these cross sections is in satisfactory accord with the single va lue measured previously at 2 keV amu(-1) in this laboratory using a di fferent technique. There have been no other experimental or theoretica l studies of the He2+-O collision system. Production of O2+ ions, main ly by transfer ionization involving one-electron capture, is surprisin gly effective with the O2+/O+ production ratio increasing from 0.23 to 0.64 over the energy range considered.