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

High energy resolution observations of the threshold region of the He(2 3S) electron excitation function have been made by monitoring the He(2 3S) 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 3S state. Measurements of the relative total metastable production cross section have been extended to cover the whole range of energies from the 2 3S 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 3S and 3 1S optical excitation functions.