Atomic data from the IRON project^*

LXVIII. Electron impact excitation of Fe xi

¹ DAMTP, Centre for Mathematical Sciences, Wilberforce Road Cambridge, CB3 0WA, UK e-mail: G.Del-Zanna@damtp.cam.ac.uk
² Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK

Received: 28 July 2009
Accepted: 11 January 2010

Abstract

A new R-matrix scattering calculation for electron collisional excitation of Fe xi is presented and compared to earlier calculations. The calculation includes 145 LS terms and 465 fine-structure levels and uses the intermediate-coupling frame transformation method (ICFT). We discuss the strong interactions that exist between three J = 1 levels in the 3s² 3p³ 3d electron configuration. These levels give rise to strong lines in the EUV spectrum and their energies and identifications have been the source of much confusion in the literature. We show that the oscillator and collision strengths linking these levels to the ground levels of the ion are very sensitive to the choice of configuration basis and argue that most earlier calculations have failed to represent these levels adequately.