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.