ABSOLUTE CROSS-SECTIONS FOR 100 EV ELECTRON-IMPACT IONIZATION OF HELIUM IN A SYMMETRICAL ENERGY-SHARING GEOMETRY

Interest in (e-2e) processes in symmetric energy-sharing geometries has been stimulated by the new experimental work of Frost et al. (1989) and the theoretical calculations of Zhang et al. (1989), and also by the method developed by Gelebart et al. (1989) for obtaining absolute cross section values. Both Frost et al. and Zhang et al. find a deep minimum in the 200 eV cross section at an angle near to theta =85’ which was not observed in earlier work by Pochat et al. (1983). The authors report absolute cross section measurements at 100 eV incident energy, over an angular range 35’ to 150’. They also find a deep minimum at 85’ and obtain generally good agreement with the calculations of Zhang et al. except that the cross sections tend to be larger than theirs in the region of the secondary maximum at around theta =110’. © 1990, IOP Publishing Ltd.