Rate coefficients for electron impact excitation of helium-like ions within the Dirac R-matrix approach

The Dirac R-matrix theory is used to calculate the collision strengths for electron impact excitation of He-like ions (S14+, Ca18+ and Fe24+) using th e Dirac atomic R-matrix code, which has been developed mainly by Norrington and Grant (Norrington P H and Grant IP 1987 J. Phys. B: At Mel. Phys. 20 4 869). The lowest 31 target levels are included in the calculation. Rate coe fficients are obtained for transitions from the ground 1s(2) S-1(0) State t o the fine-structure levels of all excited states of 1s2l (l = 0, 1) and ls 3l (l = 0, 1, 2) configurations. We compare our results for rate coefficien ts with the results of previous calculations, and indicate where significan t differences arise because of our more accurate representation of resonanc e and relativistic effects.