R-matrix electron-impact excitation data for the Mg-like iso-electronic sequence

Abstract

Aims. Emission lines from ions in the Mg-like iso-electronic sequence can be used as reliable diagnostics of temperature and density of astrophysical and fusion plasmas over a wide range of parameters. Data in the literature are quite lacking, there are no calculations for many of the ions in the sequence. Methods. We have carried-out intermediate coupling frame transformation R-matrix calculations which include a total of 283 fine-structure levels in both the configuration interaction target and close-coupling collision expansions. These arise from the configurations 1s2 2s2 2p6 3 {s,p,d} nl with n = 4,5, and for l = 0-4. Results. We obtain ordinary collision strengths and Maxwell-averaged effective collision strengths for the electron-impact excitation of all the ions of the Mg-like sequence, from Al+ to Zn18+. We compare our results with those from previous R-matrix and distorted waves calculations, where available, for some benchmark ions. We find good agreement with the results of previous calculations for the transitions n = 3-3. We also find good agreement for the most intense transitions n = 3-4. These transitions are important for populating the upper levels of the main diagnostic lines.