Atomic data from the IRON Project

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Astron. Astrophys. Suppl. Ser. 137, 175-184

Atomic data from the IRON Project

XXXVI. Electron excitation of Be-like Fe XXIII between ${\rm 1s^2}\,2l_1\,2l_2\,SLJ$ and ${\rm 1s^2}\,2l_3\,2l_4\,S'L'J'$

M.C. Chidichimo¹ - V. Zeman² - J.A. Tully³ - K.A. Berrington⁴

1 - Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
2 - Mathematics Department, University of Nottingham, Nottingham NG7 2RD, UK
3 - Département Gian Domenico Cassini, Observatoire de la Côte d'Azur, BP. 4229, 06304 Nice Cedex 4, France
4 - School of Science and Mathematics, Sheffield Hallam University, Sheffield S1 1WB, UK

Received October 19, 1998; accepted March 9, 1999

Abstract:

Partial collision strengths for electron induced transitions in the beryllium-like ion Fe XXIII are calculated using the Belfast R-matrix programs (Berrington et al. 1995). Our target has 98 fine structure states ${\rm 1s^2}\,nl\,n'l'\,SLJ$ corresponding to n = 2 and n' = 2, 3, 4. The present calculation is carried out for electron impact energies in the range 3.15 to 350 Ry. Below 115.185 Ry, corresponding to the highest excited state of our model ion, we use the Breit-Pauli version of the R-matrix code. For energies between 116 and 350 Ry we use the non-relativistic LS-coupling version of the R-matrix code together with JAJOM (Saraph 1978). When T exceeds about ten million degrees one needs to take account of contributions to the thermally averaged collision strength $\sl \Upsilon$ coming from electrons with energies in excess of 350 Ry. We discuss a way of estimating these contributions. Values of $\sl \Upsilon$ are computed and tabulated as functions of ${\rm log}\,T$ for transitions between the $\rm 2s^2\,\, ^1S_0$ , $\rm 2s2p\,\,^3P_{0,1,2}^o$ , $\rm 2s2p\,\,^1P_1^o$ , $\rm 2p^2\,\,^3P_{0,1,2}$ , $\rm 2p^2\,\, ^1D_2$ and $\rm 2p^2\,\, ^1S_0$ states. The temperature range $6.3 \le \log\, T \le 8.1$ is centred on ${\rm log}\,T = 7.1$ which, according to Arnaud & Rothenflug (1985), is where Fe XXIII has maximum coronal abundance.