Electron impact excitation of carbon-like iron

Collision strengths for transitions among the energetically lowest 46 fine-structure levels belonging to the (1s 2 ) 2s 2 2p 2 , 2s2p 3 , 2p 4 , 2s 2 2p3s, 2s 2 2p3p and 2s 2 2p3d configurations of Fe XXI are computed, over an electron energy range of 80 E 480 Ryd, using the recent Dirac atomic R -matrix code of Norrington and Grant. All partial waves with J 36.5 have been included, and a contribution of higher partial waves has been added to ensure the convergence of collision strengths for all transitions and at all energies. The results are compared with those available in the literature, and the accuracy of the data is assessed.