Continuum effects in electron-helium total cross sections

Abstract
It is shown that total cross sections for the excitation of target states with large spectroscopic factors may be calculated accurately by representing the states by their leading independent-particle configurations. With this approximation coupled-channels calculations agree only qualitatively with experimental total cross sections for the first five states of helium. R-matrix calculations using configuration interaction show better qualitative agreement. The complex polarisation potential for continuum excitations is described for two-electron atoms. When this is included in a coupled-channels optical calculation quantitative agreement with experiment is obtained for most states at 30, 50 and 100 eV.

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