Inelastic processes in He+-He collisions

Measurements are reported of the differential cross sections for excitation of inelastic processes in He + -He collisions for the range of incident ion energy E from 1 to 3 keV. The use of an improved energy analyser permits the detection of a number of inelastic channels, hitherto unresolved. In particular, the excitation of He in the (1s2p) 1.3 P state is well separated from other channels; the reactions for the formation of He + (2p) and He 2+ are studied for the first time. The results, which are given for scattering angles theta , up to 8 degrees in the laboratory system, confirm that for E>or approximately=4 kev deg. excitation occurs mainly via rotational coupling between the 2 Sigma u and 2 Pi u states and between the 2 Sigma g , 2 Pi g and 2 Delta g states of the He 2 + quasi-molecule. As for the measurements of direct ionization the oscillatory structure observed in the energy distribution of the ejected electrons for a given E, is interpreted by a crossing mechanism between the 2 Sigma g state of He + 2 and the 2 Sigma g continuum state of the system (He 2+ 2 +e).