Atomic data from the IRON Project^*

LVIII. Electron impact excitation of

¹ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK e-mail: PJS@star.ucl.ac.uk
² Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, UK
³ UMR 8102 (associée au CNRS et à l'Université Paris 7) et LUTH, Observatoire de Paris, 92195 Meudon, France

Received: 2 August 2004
Accepted: 1 November 2004

Abstract

A new calculation of rate coefficients for electron collisional excitation of is presented and compared to earlier calculations. Significant differences are found with all earlier work due to the inclusion of resonance processes that have not previously been considered and to the use of the intermediate coupling frame transformation method. The resulting dataset of collision strengths is shown to resolve many of the outstanding discrepancies between theory and solar observations. In particular, density sensitive line ratios in now indicate electron densities close to those derived from other ions of comparable ionization potential.