COLLISION STRENGTHS AND EXCITATION RATE COEFFICIENTS FOR TRANSITIONS IN FE-XXI

Using the Dirac-Fock R-matrix program, collision strengths have been computed for all transitions belonging to 20 fine-structure levels among the 1s(2)2s(2)2p2, 1s(2)2s2p3, and 1s(2)2p4 configurations of Fe XXI. All partial waves with J less-than-or-equal-to 29/2 of both even and odd parities have been included, and collision strengths are tabulated at energies above thresholds in the range below 300 Ry. Resonances are highlighted in the threshold energy region, and effective collision strengths have been obtained after integrating collision strengths over a Maxwellian distribution of electron velocities. The results for effective collision strengths are tabulated at a series of electron temperatures below log T(e) = 7.4 K suitable for applications in astrophysical and laboratory plasmas. Comparisons have been made with the earlier available distorted wave data, and accuracy is assessed. The earlier collision strengths have been underestimated up to a factor of 3 for some of the transitions, whereas effective collision strengths have been underestimated up to an order of magnitude mainly due to the omission of resonances.