Electron impact excitation of fine-structure levels in sulfur-like Fe XI

Collision strengths for electron impact excitation of fine-structure levels in sulfur-like Fe XI are calculated in a semirelativistic R-matrix approac h. The 38 fine-structure levels arising from the 20 LS states 3s(2)3p(4) P- 3, D-1, S-1; 3s3p(5) P-3(o), (1)p(o); 3s(2)3p(3)(S-4(o))3d D-3(o), 3s(2)3p( 3)(P-2(o))3d P-1,3(o), D-1,3(o), F-1,3(o), 3s(2)3p(3)(D-2(o))3d S-1,3(o), P -1,3(o), D-1,3(o), F-1,3(o) are included in our calculation. The target lev els are represented by configuration interaction wave functions. The relati vistic effects are considered in the Breit-Pauli approximation by including one-body mass correction, Darwin term, and spin-orbit terms in the scatter ing equations. Collision strengths for transitions from the 3s(2)3p(4) P-3( 2,1,0) levels to the fine-structure levels of the 3s(2)3p(3)3d configuratio n are compared with the distorted-wave results of Bhatia & Doschek at 8.0, 16.0, 24.0 ryd. There are some significant discrepancies between the two ca lculations, mostly caused by the difference in target wave functions. The c ollision strengths are integrated over a Maxwellian distribution of electro n energies to obtain effective collision strengths over the temperature ran ge from 5 x 10(5) to 5 x 10(6) K.