Modified Optical-Potential Approach to Low-Energy Electron-Helium Scattering

Abstract

A modified optical-potential approach is introduced for electron-atom scattering at low energies whereby the formal optical potential is used directly in a variational expression for scattering phase shifts. This approach has the advantage that one may include the effect of the second-order optical potential without recourse to the usual adiabatic approximation. The diagrammatic approach associated with the present method makes it possible to identify different contributing terms with different physical effects, and thus to assess the relative importance of various physical effects involved in the scattering process. To test the approach as a practical method for low-energy electron-atom scattering, we applied it to the case of electron-helium scattering for the energy range 1.2 to 16.4 eV. Good agreement with available experimental data has been obtained. The contributions of various multipole components in the second-order optical potential are examined. In particular, the effect of exchange in the second-order optical potential, neglected in most calculations, was found to be very significant.