Electron scattering by atoms and ions using the Breit-Pauli Hamiltonian: an R-matrix approach

The R-matrix method describing the scattering of low-energy electrons by complex atoms and ions is extended to include terms of the Breit-Pauli Hamiltonian. An application is made to the astrophysically important 1s²2s^{2 1}S₀^e-1s²2s2p ³P₁^o transition in Fe XXIII, where in the most accurate calculations carried out all terms of the 1s²2s², 1s²2s2p and 1s²2p² configurations are included in the expansion describing the collision. This gives up to 28 coupled channels for each total angular momentum and parity which are solved on a CRAY-1. The collision strengths are increased by more than a factor of two from their non-relativistic values at all energies considered.