Atomic data from the IRON Project. XV. Electron excitation of the fine-structure transitions in hydrogen-like ions He ii and Fe xxvi

Department of Applied Mathematics & Theoretical Physics, The Queen's University, Belfast, BT7 1NN, UK

Send offprint request to: K.A. Berrington

Received: 17 October 1995
Accepted: 6 November 1995

Abstract

Electron excitation collision strengths for fine-structure transitions involving relativistic levels with principal quantum number in hydrogen-like ions He ii and Fe xxvi are calculated using R-matrix techniques. The model target ion includes all 25 energy levels with . Low-energy collision strengths dominated by autoionizing resonances are averaged over a Maxwellian velocity distribution to obtain effective collision strengths as a function of electron temperature. In the case of He ii, such resonances enhance the collision strength by up to a factor of 3 over earlier calculations for excitation of the levels due to the presence of doubly-excited states near the thresholds. For He ii, the data are presented at four temperature points ranging from log(K) to 4.3, and for Fe xxvi from log(K) to 7.5.