ELECTRON-IMPACT EXCITATION OF MG-II - COLLISION STRENGTHS AND RATE COEFFICIENTS

Collision strengths for low-energy electron-impact excitation of Mg It are computed in a ten-state close-coupling approximation using the R- matrix method. Fine-structure transitions among the 17 associated leve ls are considered explicitly through algebraic transformation of the s cattering matrices. Detailed comparisons are made with the merged-beam experiment of Smith and co-workers and the crossed-beam experiment of Zapesochnyi and co-workers; the present results are found to be in ve ry good agreement with the former for the 3s-3p resonance transition. A comparison with earlier theoretical calculations is also made. Maxwe llian-averaged rate coefficients are calculated for transitions betwee n the target levels considered, and a selection of these results is pr esented for practical applications.