Electron impact excitation rates for transitions in beryllium-like ions between Sc XVIII and Zn XXVII

Abstract

Electron impact excitation rates for the Be-like ion Si XI, Ca XVII and Fe XXIII, calculated with the R-matrix code, are used to interpolate or extrapolate data for the ions between Sc XVIII and Zn XXVII. Results for all 45 transitions among the 2s2 1S; 2s2p3P, 1P; 2p2 3P, 1D and 1S levels are presented in the form of polynomial fits in log Te to the effective collision strengths (γ) for each transition. These fits lead to results accurate to an estimated ± 10%, and are applicable over a temperature range of log Tmax ± 0.8 dex, where Tmax is the temperature of maximum fractional abundance in ionization equilibrium of the relevant species. Significant differences between the present results and the earlier distorted-wave calculations of Bhatia et al. for Ti XIX and Ni XXV are found for some transitions.