Electron impact ionization of helium at intermediate collision energies

Abstract
Triple differential cross sections for the single ionization of helium by 400 eV, 250 eV and 150 eV electrons have been measured in the range of momentum transfer from 0.35 to 1.1 atomic units. The large number of measurements covers most of the dynamical situations under which electron impact ionization for a given impact energy can occur. The measurements therefore serve as a rather complete set of data for comparison with theory. Several second-order theories have been tested. A second Born approximation with an improved wavefunction for the low-energy ejected electron is most suitable to describe the process.