ELECTRON-IMPACT EXCITATION OF FE2+ .1. A 17-LEVEL FINE-STRUCTURE CALCULATION

A Breit-Pauli R-matrix calculation for the electron impact collision strengths of Fe2+ is reported involving transitions among the lowest 17 levels corresponding to the 3d6 5D, H-3, 3P, 3F and 3G terms. Resonance structures are elucidated for the first time. The calculated collision strengths at impact energies above the resonance region show some disagreements with those from an earlier five-term R-matrix calculation of Garstang et al, for example the 5D-H-3 and H-3-3P collision strengths are a factor of three larger than in the earlier calculation. The present calculation also investigates the variation of collision strengths with energy; in particular, resonances are found to enhance the thermally averaged effective collision strengths by up to 40% for transitions among the fine-structure levels of the 5D ground state. Effective collision strengths for all transitions among the 17 levels are tabulated for electron temperatures 10 000 K and 20 000 K.