Inelastic processes in He+-He collisions

Abstract

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) ^1.3P state is well separated from other channels; the reactions for the formation of He⁺(2p) and He²⁺ 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 He₂⁺ 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 (He²⁺₂+e).