The electron-helium scattering system is studied within the S-wave framework with a particular emphasis on one-electron ionization processes. Total ionization and the singly differential cross section for the equal-energy-sharing point are given for three initial states. In addition, discrete excitation cross sections are also given. Whereas generally there is no a priori relationship between cross sections for excitation of corresponding singlet and triplet states, we find that for the case of ionization with equal-energy outgoing electrons the triplet cross section is approximately three times bigger than the corresponding singlet one, irrespective of the initial state or energy.

• Received 5 August 2001

DOI:https://doi.org/10.1103/PhysRevA.65.032701