A possible contribution to the population of triplet states in electron impact measurements of total cross sections for triplet state excitation

Abstract

It is proposed that low energy secondary electrons produced in medium energy electron impact experiments may play an important role in the excitation of triplet states even at low sample gas densities. A model calculation is carried out which shows that the population of the 4 3S, S 3P and 4 3D triplet states in He from secondary electron excitation can be comparable to the population of these states by direct excitation at an incident electron energy of 1000 eV and sample gas pressures as low as 10 −3 torr. The model calculations show that the secondary electron mechanism becomes more important as the incident energy increases and that the produced populations are of a similar magnitude for the 3 3P and 4 3D states which in turn are about a factor of 4 larger than the population found for the 4 3S state. The results indicate that the effect of secondary electron excitation in careful experimental measurements of electron impact total triplet state cross sections may have to be considered when incident electron excitation energies in the range of 1 keV or higher are used.