Exicitation mechanisms in He+-He collisions

Single-electron excitation of He atoms by 30 and 50 keV He+ impact was investigated using anticrossing spectroscopy. The measured anticrossing spectra give evidence for the assumption that in the intermediate energy range, where the excitation cross-sections have resonance-like maxima, excitation proceeds via Paul-trap promotion. The electron to be excited gains energy by transiently riding during the collision on the saddle of the two-center potential of the (He+)(2) molecular core.