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

L. Fernández-Menchero, G. Del Zanna, N.R. Badnell

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Abstract

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 fine-structure levels in both the configuration interaction target and close-coupling collision expansions. These arise from the configurations 1s2 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 Zn26+. 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.
Original languageEnglish
Article numberA104
Number of pages11
JournalAstronomy and Astrophysics
Volume566
Early online date23 Jun 2014
DOIs
Publication statusPublished - 2014

Keywords

  • atomic data
  • astrophysical plasma
  • fusion plasma
  • collision strengths

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