Atomic data from the IRON project

LX. Electron-impact excitation of n = 3, 4 levels of Fe

¹ Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK e-mail: witthoeft@phys.strath.ac.uk
² MSSL, University College London, Holmbury St., Mary Dorking, RH5 6NT, UK
³ School of Science and Mathematics, Sheffield Hallam University, Sheffield, S1 1WB, UK
⁴ Gatsby Computational Neuroscience Unit, University College, 17 Queen Square, London, WC1N 3AR, UK

Received: 14 June 2005
Accepted: 1 September 2005

Abstract

We present results for electron-impact excitation of F-like Fe calculated using R-matrix theory where an intermediate-coupling frame transformation (ICFT) is used to obtain level-resolved collision strengths. Two such calculations are performed, the first expands the target using 2s² 2p⁵, 2s 2p⁶, 2s² 2p^{4 3l}, 2s 2p^{5 3l}, and 2p^{6 3l} configurations while the second calculation includes the 2s² 2p^{4 4l}, 2s 2p^{5 4l}, and 2p^{6 4l} configurations as well. The effect of the additional structure in the latter calculation on the resonances is explored and compared with previous calculations. We find strong resonant enhancement of the effective collision strengths to the 2s² 2p⁴ 3s levels. A comparison with a Chandra X-ray observation of Capella shows that the R-matrix calculation leads to good agreement with observation.