Ionization: Test of a continuum optical model for electron scattering

An optical potential for taking account of the continuum in a coupled-channels calculation of electron scattering from atoms and ions must reproduce the total ionization cross section. This is tested here for a range of atoms and ions, using a momentum-space formulation based on the orthogonalized Born-Oppenheimer approximation to the ionization amplitude. The theory is quite acceptable as a fast calculation of total ionization cross sections, particularly at higher energies where distorted-wave methods are cumbersome. It compares quite satisfactorily with distorted-wave calculations for ions at lower energies near the maximum of the cross-section curve.