EDP Sciences
Free access
Volume 481, Number 2, April II 2008
Page(s) 543 - 551
Section Atomic, molecular, and nuclear data
DOI http://dx.doi.org/10.1051/0004-6361:20079073
Published online 25 January 2008

A&A 481, 543-551 (2008)
DOI: 10.1051/0004-6361:20079073

Atomic data from the IRON Project

LXV. Electron-impact excitation of Fe6+
M. C. Witthoeft1, 2 and N. R. Badnell1

1  Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK
2  NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
    e-mail: witthoef@milkyway.gsfc.nasa.gov

(Received 15 November 2007 / Accepted 16 January 2008)

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.

Key words: atomic data

© ESO 2008