2014MNRAS.442..388A

Energies for the lowest 56 levels, belonging to the 3s23p, 3s3p2, 3p3, 3s23d, 3s3p3d, 3s2 4ℓ and 3s2 5ℓ configurations of SIII, are calculated using the General-purpose Relativistic Atomic Structure Package (grasp) code. Analogous calculations have also been performed (for up to 175 levels) using the Flexible Atomic Code (fac). Furthermore, radiative rates are calculated for all E1, E2, M1 and M2 transitions. Extensive comparisons are made with available theoretical and experimental energy levels, and the accuracy of the present results is assessed to be better than 0.1Ryd. Similarly, the accuracy for radiative rates (and subsequently lifetimes) is estimated to be better than 20 per cent for most of the (strong) transitions. Electron impact excitation collision strengths are also calculated, with the Dirac Atomic R-matrix Code (darc), over a wide energy range up to 13Ryd. Finally, to determine effective collision strengths, resonances are resolved in a fine energy mesh in the thresholds region. These collision strengths are averaged over a Maxwellian velocity distribution and results listed over a wide range of temperatures, up to 10^5.5K. Our data are compared with earlier R-matrix calculations and differences noted, up to a factor of 2, for several transitions. Although scope remains for improvement, the accuracy for our results of collision strengths and effective collision strengths is assessed to be about 20 per cent for a majority of transitions.