Total reaction cross sections in the atomic coupled-channels optical model

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Abstract
A coupled-channels optical model for intermediate-energy electron scattering on hydrogen is constructed for 1, 3, 4 and 6 states by using first-order direct and exchange real potentials and an imaginary potential proportional to the density matrix with strength chosen to reproduce the ground-state total reaction cross section. This reaction cross section is linear in the strength parameter. The weak-coupling approximation is valid in the sense that the cross section for reactions to channels outside the computation space is given by a one-channel calculation with the appropriate potential. The three state (1s-2s-2p) close-coupling results are used to deduce the ionisation cross sections from the 1s state at energies from 30 to 200 eV. The results are in reasonable agreement with experiment. The same potential may be used to obtain a close approximation to the ionisation cross section using a one-channel model.