Zero Angle Energy Losses in Helium

Abstract

Inelastic electron scattering at 0° has been studied in helium with an electrostatic analyzer. Below 100 volts, four energy losses have been identified and studied: the $1{}_{}{}^1{}_{}{}^{}S-2\mathrm{}{}_{}{}^1{}_{}{}^{}P$, $1{}_{}{}^1{}_{}{}^{}S-3\mathrm{}{}_{}{}^1{}_{}{}^{}P$, $1{}_{}{}^1{}_{}{}^{}S-2\mathrm{}{}_{}{}^1{}_{}{}^{}S$, and $1{}_{}{}^1{}_{}{}^{}S-2\mathrm{}{}_{}{}^3{}_{}{}^{}S$. The probabilities of these losses relative to the $1{}_{}{}^1{}_{}{}^{}S-2\mathrm{}{}_{}{}^1{}_{}{}^{}P$ loss have been determined, and these ratios compared with theoretical values. The ratio for the $1{}_{}{}^1{}_{}{}^{}S-3\mathrm{}{}_{}{}^1{}_{}{}^{}P$ is in good agreement with theory; that for the $1{}_{}{}^1{}_{}{}^{}S-2\mathrm{}{}_{}{}^1{}_{}{}^{}S$ is not. The relative probability of the $1{}_{}{}^1{}_{}{}^{}S-2\mathrm{}{}_{}{}^1{}_{}{}^{}P$ loss has been measured from 50-150 volts. It exhibits a maximum at 75 volts and a rapid decrease down to 40 volts. Above 100 volts it is in general agreement with other experimental results.