R-matrix theory of electron scattering at intermediate energies

A new R-matrix theory of electron-atom and electron-molecule scattering at intermediate energies is described. In this theory both the outer valence electron of the target atom or molecule and the scattered electron are expanded in terms of a continuum R-matrix basis. This enables target eigenstates as well as pseudostates representing inelastic effects to be accurately represented in an internal region. In addition, a two-dimensional R-matrix propagator approach is developed that enables the internal region to be subdivided and highly excited target states that extend out to large distances to be treated. This new theory is then combined with the T-matrix energy averaging technique introduced earlier by Burke et al. (1981) to yield accurate cross sections at intermediate energies. The method is illustrated by applying it to the elastic s-wave scattering of electrons by atomic hydrogen from threshold to 60 eV. (author)