Benchmark calculations for near-threshold electron-impact excitation of krypton and xenon atoms

The recently developed semi-relativistic Breit-Pauli and fully relativistic Dirac-Coulomb versions of the B-spline R-matrix (close-coupling) approach with non-orthogonal orbitals have been used to calculate electron-impact excitation of the 4p(5)5s states in Kr and the 5p(5)6s states in Xe. Comparison of the predictions shows a substantial improvement in the agreement between theory and experiment over that achieved in previous semi-relativistic Breit-Pauli R-matrix calculations. For the Xe target, a fully relativistic treatment appears to be essential in the quest to quantitatively reproduce the wealth of near-threshold resonance features. While the overall agreement in the measured and calculated energy dependence of the angle-integrated and the angle-differential cross sections is excellent, some unexplained discrepancies of up to 50% remain regarding the absolute normalization.