Paper XXXVI

Electron excitation of Be-like Fe XXIII between 1s$^2$2$l_12l_2$ SLJ and 1s$^2$2$l_32l_4$ SLJ

M.C. Chidichimo, V. Zeman, J.A. Tully and K.A. Berrington

Astronomy & Astrophysics Supplement Series, 1999, Vol.137, pp.175-184

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 1s $^2nln^\prime l^\prime$ SLJ corresponding to $n=2$ and $n^\prime=2,3,4$. 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 $\Upsilon$ coming from electrons with energies in excess of 350 Ry. We discuss a way of estimating these contributions. Values of $\Upsilon$ are computed and tabulated as functions of $\log T$ for transitions between the 2s$^2$ $^1$S$_0$,2s2p$^3$P $^\circ_{0,1,2}$, 2s2p$^1$P$^\circ_{1}$, 2p$^2$ $^3$P$_{0,1,2}$,2p$^2$ $^1$D$_{2}$ and 2p$^2$ $^1$S$_{0}$ states. The temperature range $6.3\le \log T \le 8.1$ is centred on $\log T = 7.1$ which according to Arnaud & Rothenflug (1985), is where Fe XXIII has maximum coronal abundance.