Aims. Emission lines from ions in the Be-like isoelectronic sequence can be used for reliable diagnostics of temperature and density of astrophysical and fusion plasmas over a wide range of temperatures. Surprisingly, interpolated data is all that is available for a number of astrophysically important ions. Methods. We have carried out intermediate coupling frame transformation R-matrix calculations which include a total of 238 finestructure levels in both the configuration interaction target and close-coupling collision expansions. These arise from the configurations 1s 2 2{s, p} nl with n = 3−7, and l = 0−4 for n ≤ 5 and l = 0−2 for n = 6, 7. Results. We obtain ordinary collision strengths and Maxwell-averaged effective collision strengths for the electron-impact excitation of all the ions of the Be-like sequence, from B + to Zn 26+ . We compare with previous R-matrix calculations and interpolated values for some benchmark ions. We find good agreement for transitions n = 2−2 with previous R-matrix calculations but some disagreements with interpolated values. We also find good agreement for the most intense transitions n = 2−3 which contribute via cascade to the (n = 2) diagnostic radiating levels.

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 finestructure levels in both the configuration interaction target and close-coupling collision expansions. These arise from the configurations 1s 2 2s 2 2p 6 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 Zn 18+ . 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.

We have carried-out 98-level configuration-interaction / close-coupling (CI/CC) intermediate coupling frame transformation (ICFT) and Breit-Pauli R-matrix calculations for the electron-impact excitation of Be-like Al 9+ . The close agreement that we find between the two sets of effective collision strengths demonstrates the continued robustness of the ICFT method. On the other hand, a comparison of this data with previous 238-level CI/CC ICFT effective collision strengths shows that the results for excitation up to n = 4 levels are systematically and increasingly underestimated over a wide range of temperatures by R-matrix calculations whose close-coupling expansion extends only to n = 4 (98-levels).Thus, we find to be false a recent conjecture that the ICFT approach may not be completely robust. The conjecture was based upon a comparison of 98-level CI/CC Dirac R-matrix effective collision strengths for Al 9+ with those from the 238-level CI/CC ICFT R-matrix calculations. The disagreement found recently is due to a lack of convergence of the closecoupling expansion in the 98-level CI/CC Dirac work. The earlier 238-level CI/CC ICFT work has a superior target to the 98-level CI/CC Dirac one and provides more accurate atomic data.Similar considerations need to be made for other Be-like ions and for other sequences.

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