Paper XLI

Electron impact excitation rates among the 3d$^2$ fine-structure levels of Ca-like Fe sc vii

K.A. Berrington, S. Nakazaki, and P.H. Norrington

Astronomy & Astrophysics Supplement Series, 2000, Vol.142, pp.313-316

Electron excitation collision strengths of 3d$^2$ fine-structure transitions in Ca-like Fe sc vii are calculated using an R-matrix method, which included the 80 terms arising form the 3d$^2$, 3d4s, 3d4p, 3d4d, 3d4f and 3p$^5$3d$^3$ configurations. Extensive autoionizing resonance structures together with channel coupling is therefore explicitly included: relativistic effects are accounted for by a term-coupling transformation. A thermal average is taken to obtain the effective fine-structure collision strength as a function of electron temperature T, for $\log T$(K)$=4.3$-6. Open 3p-shell resonances are seen to considerably enhance the background collision strength, by several factors for some of the 3d $^2_{j\rightarrow j^\prime}$ transitions.