Excitation of the 3p~55p levels of argon from the 3p~54s metastables

摘要

Measurements have been reported recently of cross sections for electron-impact excitation of the argon 3p~55p manifold of levels from the 3p~54s metastable levels. We report results of calculations of the direct excitation cross sections at electron-impact energies from threshold to 500eV for these transitions. The collision cross sections are calculated in the scaled plane-wave Born approximation (scaled PWB) developed by Kim. This scaling transforms the Born cross sections for dipole-allowed and spin-allowed excitations into reliable cross sections that compare as well with accurate measurements as does the sophisticated and more complex convergent close coupling method. We have used jj coupling in a single LS configuration Dirac-Fock calculation to describe the target wavefunctions. The optical emission cross section measurements, by Jung et al., include estimated contributions of 25% or more from cascading from higher excited levels and so are larger than direct excitation cross sections. Nevertheless, our cross sections agree reasonably well with the measurements for transitions where the core j value remains unchanged, except for the 1s_5-3p_8 excitation. The results do not agree well with the measurements when the core j value changes, as similarly seen in the results of recent relativistic distorted wave calculations by Sharma et al.