Rate coefficients for electron impact excitation of helium-like ions

Abstract

The distorted wave (DW) approximation is used to solve the e(+) ion scattering problem. It is found that for He-like ions the DW approximation, which neglects coupling between states other than the initial and the final, compares extremely well with the more elaborate close-coupling approximation. Rate parameters gamma(T) are presented for all 10 transitions involving the ground state and the n=2 states, for He-like Be, C, O, Ne, Si, Ca, and Fe. The rate parameters were obtained from collision strengths calculated and fitted to expressions in energy, separately in a number of different energy intervals. In terms of the variation with temperature T, the results gamma(T), may be divided into three categories corresponding to forbidden, intercombination, and allowed transitions.