Paper LII

Electron excitation of Ni$^{+24}$

M.C. Chidichimo, N.R. Badnell and J.A. Tully

Astronomy & Astrophysics, 2003, Vol.401, p 1177

This paper reports on the calculation of collision strengths for electron induced transitions in the beryllium-like ion Ni XXV whose ground state is 1s$^2$ 2s$^2$ $^1$S[0]. We make use of the R-matrix method in conjunction with the intermediate frame coupling transformation (IFCT). The target has 98 fine structure states 1s$^2$ nl n'l' SLJ corresponding to n = 2 and n' = 2, 3, 4 . Our calculation extends up to 440 Ry with respect to the ground state. In order to obtain reliable rate coefficients at high temperatures (T above 2 x 10$^7$ K) we have extended our collision strengths to much higher energies by using a variety of techniques, including use of Burgess's interactive code OmeUps. The effective collision strength Upsilon is tabulated against log T for the 45 transitions linking the lowest 10 levels. We also give results for 5 transitions in the X-ray region which are needed in solar studies. The temperature range 6.3 <=log T <=8.3 is centred on log T = 7.1 which is where this ion has its maximum coronal abundance.

Figures 1 to 8, and Appendix A are only available in electronic form at http://www.edpsciences.org