Electron impact ionisation of Fe XXIV ions

The electron impact ionization cross section of Fe XXIV is calculated by two methods, both making allowance for excitation-autoionization and for radiative decay. It is found that the breakdown of LS coupling for this ion does not seriously affect the results but that the effects of radiative decay are to reduce the excitation-autoionization contribution by a significant amount. The results obtained omitting radiative decay are up to 25 percent larger than those given by the semi-empirical formula of Burgess and Chidichimo (1983), which also omits this process.