R-matrix theory for electron-atom and electron-molecule collisions using analytic basis set expansions

A formulation of R-matrix theory based on analytic basis set expansions of the internal wavefunction is presented which has several advantages over the more conventional approach. Integral evaluation is simple even for diatomic molecules, the R-matrix boundary condition is incorporated into the hamiltonian not the basis functions and single-center expansions are eliminated for non-spherical targets. Results for electron-He scattering are presented and compared with other calculations to illustrate the technique.