Inelastic collisions of metastable helium on helium at impact energies between 1000 and 5000 eV

Abstract

Elastic and inelastic collisions of metastable He* atoms on He have been investigated experimentally by electrostatic energy analysis of electrons and ions arising from the collisions, and by time-of-flight analysis of the scattered neutrals. Collision energies were between 1000 and 1400 eV in case of He+ and He analysis and up to 5000 eV for the electron analysis. Excitation of autoionising He states was observed in all spectra. Contributions to the spectra due to collisions of ground-state atoms, which were also contained in the beam, could be identified and thus relative differential cross sections for pure He*-He scattering were determined for reduced scattering angles tau >or approximately=2.5 keV deg. Scattered ions were only analysed at a scattering angle of Theta =8 degrees and therefore the authors could not investigate ionisation processes leading mainly to small scattering angles, e.g. the direct coupling into the ionisation continuum He++He+e-, which was investigated earlier by Gillen et al. (1977).