THEORY AND PRACTICE IN LOW-ENERGY-ELECTRON EXCITATION OF THE 5P(5)6S LEVELS OF XENON

This letter concerns low-energy electron excitation from the ground st ate of xenon (5p(6 1)S(0)) to the lowest four excited levels (5p(5)6s P-3(0.1.2) and P-1(1)). We report here on the first results from Breit -Pauli R-matrix theory which investigates coupling to the 6p and 5d le vels: specifically, in 5-, 15- and 22-level calculations. Differential cross sections at 15 eV are compared with other theories and with exp eriments. Our present 22-level R-matrix calculation represents the mos t elaborate on this system to date and gives reasonable agreement with experiments, though some discrepancies remain. We note that perturbat ive approaches such as recent distorted-wave calculations agree less w ell with experiments, and we conclude from this and from other evidenc e that such methods, as currently formulated, are not reliable for des cribing low-energy scattering from neutral systems. On the other hand, the R-matrix method appears to be capable of systematic improvement v ia the introduction of further states and pseudostates.