Effective collision strengths for Cl II

The B-spline basis has been used in the R-matrix approach to calculate electron impact excitation collision strengths for transitions between the 3s^2^3p^4^ ^3^P_0,1,2_, ^1^D_2_ and ^1^S_0_ levels and from these levels to the fine-structure levels of the excited 3s3p^5^, 3s^2^3p^3^4s, 3s^2^3p^3^3d, 3s^2^3p^3^4p and 3s^2^3p^3^4d configurations of Cl II. We considered 23 LS states 3s^2^3p^4^ ^3^P, ^1^D, ^1^S, 3s3p^5^ ^3^P^o^, 3s^2^3p^3^(^4^S^o^)4s ^5,3^S^o^, 3s^2^3p^3^(^4^S^o^)3d ^5,3^D^o^, 3s^2^3p^3^(^2^D^o^)3d ^1^P^o^, ^1^S^o^, ^3^F^o^, ^3^D^o^, ^3^P^o^, 3s^2^3p^3^(^2^D^o^)4s ^3,1^D^o^, 3s^2^3p ^3^(^2^P^o^)4s ^3,1^P^o^, 3s^2^3p^3^(^4^S^o^)4p ^5,3^P, 3s^2^3p^3^(^2^P^o^)3d ^3,1^P^o^, ^3^D^o^ and 3s^2^3p^3^(^2^D^o^)4d ^3^P^o^ in the close- coupling expansion that give rise to 51 fine-structure levels.

The non-orthogonal orbitals are used for an accurate representation of both the target wavefunctions and the R-matrix basis functions. The collision strengths for transitions between fine-structure levels are calculated by transforming the LS-coupled K-matrices to K-matrices in an intermediate coupling scheme. The Rydberg series of resonances converging to excited state thresholds make substantial contributions to collision strengths.