Atomic data and spectral line intensities for S IX

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for the O-like ion S IX. The configurations used are 2s(2)2p(4) 2s2p5, 2p(6), 2s(2)2p(3)3s, 2s(2)2p(3)3p, and 2s(2)2p(3)3d giving rise to 86 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 25, 50, 75, 100, and 125 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at several electron temperatures in the 5.6 less than or equal to log T-e (K) less than or equal to 6.2 range, where S IX is formed. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(8)-10(14) cm(-3). Relative spectral line intensities are calculated. Proton excitation rates among the lowest three levels have been included in the statistical equilibrium equations. The predicted S IX line intensities are compared with SUMER (SOHO) observations of the quiet Sun. (C) 2003 Elsevier Inc. All rights reserved.