LOW-ENERGY-ELECTRON SCATTERING FROM CESIUM ATOMS COMPARISON OF A SEMIRELATIVISTIC BREIT-PAULI AND A FULL RELATIVISTIC DIRAC TREATMENT

The discrepancies between a previous Breit-Pauli R-matrix calculation by Scott et al and a recent calculation using the Dirac Hamiltonian by Thumm and Norcross are further analysed and partially resolved. When comparable methods are applied to obtain the best possible target description in both approaches, a reduced Breit-Pauli formulation, with only the one-body spin-orbit operator included to account for relativistic effects explicitly, seems sufficient for an accurate description of most of the low-energy collision processes in this system. There remain, however, some interesting differences between the Breit-Pauli and the Dirac results for spin polarization and asymmetry functions, as well as for very sensitive resonance parameters. To shed more light on the possible origin of these differences, the effect of including additional close-coupling channels on the results is investigated.