Atomic data and spectral line intensities for S XIII

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for S XIII. The configurations used are 2s², 2s2p, 2p², 2l3l′, 2l4l′ and 2s5l′, with l = s, p and l′ = s, p, d, giving rise to 92 fine-structure levels in intermediate coupling. Collision strengths are calculated at seven incident energies (10, 20, 45, 90, 135, 180, and 225 Ry) for the transitions within the three lowest configurations, and five incident energies (45, 90, 135, 180, and 225 Ry) for transitions between the lowest five levels and the n = 3, 4, 5 configurations. Calculations have been carried out using the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, and R-matrix results for the 2s², 2s2p, 2p² configurations available in the literature, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10⁸-10¹⁴ cm⁻³ at an electron temperature of log T_e(K) = 6.4, corresponding to the maximum abundance of S XIII. Spectral line intensities are calculated, and their diagnostic relevance is discussed. Observed line ratios indicate electron temperatures of the emitting plasma close to log T_e(K) = 6.4. This dataset will be made available in the next version of the CHIANTI database.