Electron-impact excitation of the resonance transition inCa+

Abstract

Detailed calculations of the electron-impact excitation of ${\mathrm{Ca}}^{+}$ are performed using both perturbation theory and the close-coupling approach. Particular attention is focused on the resonance (4s-4p) excitation since experimental emission-cross-section data are available for this transition. The results of the most sophisticated model, a six-state (4s, 3d, 4p, 5s, 4d, 5p) close-coupling calculation with semiempirical Hartree-Fock target wave functions and including one- and two-body core-polarization potentials are in better agreement with the experimental cross section and resonance-fluorescence polarization data than any other calculation. At incident electron energies below the 5s, 4d, and 5p thresholds, the six-state calculations are essentially in agreement with the experimental data, although rich resonance structures predicted by theory are not seen experimentally due to the finite energy resolution. At energies above the 5s, 4d, and 5p thresholds the six-state emission cross sections exceed the experimental cross sections by about 20%, once allowance is made for cascades from the 5s, 4d, and 5p levels.