Cross sections for excitation and ionization in e-He(2sup(1,3)S) collisions

Cross sections for the 23S-n3L(n = 2-5, L = S-F) excitations and for single ionization in e-He(2sup(1,3)S) collisions are determined by using the Born approximation. For a given n, the 23S-n3D transitions dominate at intermediate energies and this trend is continued for transitions to the near continuum. For larger energies epsilon of the ejected electron, high angular momentum l waves progressively dominate. While up to nine partial waves are in general required for convergence of the bound-free form factor, as many as 30 are needed when momentum changes are in the vicinity of the Bethe ridge for large epsilon. Binary-encounter results for ionization are also obtained and agree with the Born values at intermediate energies. The present calculations and the recent measurements of Dixon et al. (J. Phys. B. Atom. Molec. Phys.; 9:2617 (1976)) are in satisfactory accord at intermediate energies. The contributions to ionization arising from multiple processes are also discussed. (author)