C II emission lines formed in optically thin plasmas

New Einstein A-coefficients and electron impact collision rates are presented for transitions between the three lowest LS states of C II. The former are based on complex configuration interaction wave functions, while the latter use such wave functions in an eight-state R-matrix calculation of the collision process. These new atomic data are then used to calculate populations for the corresponding seven fine-structure levels on the assumption of an isotropic optically thin plasma. Theoretical emission-line intensity ratios deduced from these populations are in excellent agreement with observed low- and high-density limits.