Near-threshold absolute angle-differential cross sections for electron-impact excitation of argon and xenon

Absolute angle-differential cross sections for electron-impact excitation of argon and xenon atoms to the lowest four np⁵(n+1)s levels, and the 5p⁵5d[7∕2]₃ level in xenon, have been measured and calculated as a function of electron energy up to a few eV above threshold at a fixed scattering angle of 135^∘. For argon, very good agreement is observed between the experimental data and predictions from a Breit-Pauli B-spline R-matrix (BSR) method, in which nonorthogonal orbital sets are used to optimize the target description. The agreement is still satisfactory for the more complex xenon target, suggesting that predictions from the BSR model should already be sufficiently accurate for many modeling applications. Nevertheless, the remaining discrepancies indicate the need for further refinement of the theoretical model.