Time-dependent close-coupling calculations for the electron-impact ionization of helium

Electron-impact ionization cross sections for helium are calculated using time-dependent close-coupling theory. In a frozen-core approximation, the wave function for the three-electron system is expanded in terms of two-electron wave functions which fully describe the ejected and scattered electrons at all times following the collision. The resulting close-coupled partial differential equations for the two-electron radial wave functions include a direct and a local approximation to the exchange interactions with the remaining core electron. By direct projection of the time-dependent wave functions onto continuum lattice eigenstates, both ejected energy differential and total integrated cross sections are extracted. The agreement between theory and previous experimental measurements for helium is excellent.