Abstract
We present R-matrix results for the electron-impact excitation of Fe6+. The intermediate-coupling frame transformation (ICFT) method has been used to obtain level-resolved collision strengths. We then calculate effective collision strengths assuming a Maxwellian distribution for the incident electron velocities. A large configuration interaction (CI) expansion of 1896 LS terms (4776 fine-structure levels) is used to obtain an accurate target. This is reduced to 89 close-coupling (CC) terms (189 levels) for the scattering calculation. To investigate the importance of CI, we also perform a second calculation with the same CC expansion but a smaller CI expansion. We discuss the difficulties of such a comparison and look at which transitions show the most sensitivity to the CI expansion. Our effective collision strengths are compared with a previous IRON Project report (Berrington et al. 2000, A&A, 142, 313) for transitions within the ground configuration and a recent distorted wave calculation (Zeng et al. 2005, MNRAS, 357, 440) for transitions to excited configurations. We find good agreement with the results of the previous R-matrix calculation and with the high-temperature distorted-wave results for most transitions, although there are some significant differences at lower temperatures in the latter case.
Original language | English |
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Pages (from-to) | 543-551 |
Number of pages | 8 |
Journal | Astronomy and Astrophysics |
Volume | 481 |
Issue number | 2 |
DOIs | |
Publication status | Published - Apr 2008 |
Keywords
- atomic data
- intermediate-coupling frame transformation
- Maxwellian distribution
- configuration interaction