High resolution studies of electron excitation V. The metastable states of helium

Abstract

High energy resolution observations of the threshold region of the He(2 $^{3}$S) electron excitation function have been made by monitoring the He(2 $^{3}$S) metastable flux. Structure has been observed in the total cross section very close to threshold which is interpreted as resonant s-wave scattering from the 2 $^{3}$S state. Measurements of the relative total metastable production cross section have been extended to cover the whole range of energies from the 2 $^{3}$S threshold to the ionization potential and the resonant structures associated with the $n=3$ and $n=4$ states correlated with those observed in the 3 $^{3}$S and 3 $^{1}$S optical excitation functions.