Atomic data from the IRON Project LII. Electron excitation of Ni~(+24)

摘要

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 ~1S_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 n/n'l' S LJ 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 * 10~7 K) we have extended our collision strength to much higher energies by using a variety of techniques, including use of Burgess's interactive code OmeUps. The effective collision strength γ is tabulated against logT for the 45 transitions linking the lowest to levels. We also give result 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 logT = 7.1 which is where this ion has its maximum coronal abundance.