Electron-impact excitation of argon at intermediate energies

Abstract

Large-scale $R$-matrix-with-pseudostates calculations for electron collisions with argon atoms, using a recently developed parallel version of our B-spline $R$-matrix code, are reported. The calculations were carried out in the semirelativistic $\mathit{jK}$-coupling scheme. They are intended to provide converged (with respect to the number of coupled states) results for electron-impact excitation of individual target states with dominant configurations $3{p}^{5}4s$, $3{p}^{5}4p$, $3{p}^{5}3d$, and $3{p}^{5}5s$ for incident electron energies from threshold to 300 eV. The close-coupling expansion includes 500 target states, with the lowest 78 states representing the bound spectrum and the remaining 422 the ionization continuum. The results reveal dramatic reductions of the predicted excitation cross sections at intermediate energies due to a strong influence of coupling to the target continuum and the higher-lying Rydberg states. Comparison with available experimental data for excitation raises questions about the absolute normalization in the measurements.