Effective collision strengths for electron impact excitation of fine-structure levels in Fe XI

Collision strengths for transitions between the 3s(2)3p(4) P-3(2,1,0), D-1( 2), and S-1(0) levels and from these levels to the 3s3p(5) (3)p(2,1,0,)degr ees and (1)P(1)degrees levels of Fe XI are calculated using a semirelativis tic R-matrix approach. The 38 fine-structure levels arising from the 20 LS 3s(2)3p(4) P-3, D-1, S-1, 3s3p(5) P-3 degrees, P-1 degrees, 3s(2)3p3(S-4 de grees)3d D-3 degrees, 3s(2)3p(3)((2)p degrees)3d P-1,P-3 degrees D-1,D-3 de grees, F-1,F-3 degrees, 3S(2)3p(3)(D-2 degrees)3d S-1,S-3 degrees, (1,3)p d egrees, D-1,D-3 degrees, F-1,F-3 degrees states are included in our calcula tion. These target levels are represented by configuration-interaction wave functions. The relativistic effects are considered in the Breit-Pauli appr oximation by including one-body mass correction, Darwin term, and spin-orbi t terms in the scattering equations. Complicated resonance structures are f ound to enhance the collision strengths significantly for many transitions in the threshold energy regions. Our collision strengths are compared with the available results of Bhatia & Doschek at 8.0, 16.0,and 24.0 ryd. The co llision strengths are integrated over a Maxwellian distribution of electron energies to give effective collision strengths over a wide temperature ran ge.