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Description
Collision strengths for electron impact excitation of fine-structure levels in sulfur-like Fe XI are calculated in a semirelativistic R-matrix approach. The 38 fine-structure levels arising from the 20 LS states 3s^2^3p^4^ ^3^P, ^1^D, ^1^S; 3s3p^5^ ^3^P^0^, ^1^P^0^; 3s^2^3p^3^(^4^S^0^)3d ^3^D^0^, 3s^2^3p^3^(^2^P^0^)3d ^1,3^P^0^, ^1,3^D^0^, ^1,3^F^0^, 3s^2^3p^3^(^2^D^0^)3d ^1,3^S^0^, ^1,3^P^0^, ^1,3^D^0^, ^1,3^F^0^ are included in our calculation. The target levels are represented by configuration interaction wave functions. The relativistic effects are considered in the Breit-Pauli approximation by including one-body mass correction, Darwin term, and spin-orbit terms in the scattering equations. Collision strengths for transitions from the 3s^2^3p^4^ ^3^P_2,1,0_ levels to the fine-structure levels of the 3s^2^3p^3^3d configuration are compared with the distorted-wave results of Bhatia & Doschek (1996) at 8.0, 16.0, 24.0 ryd. There are some significant discrepancies between the two calculations, mostly caused by the difference in target wave functions. The collision strengths are integrated over a Maxwellian distribution of electron energies to obtain effective collision strengths over the temperature range from 5x10^5^ to 5x10^6^ K.
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