Atomic Data and Spectral Line Intensities for Si VII

Abstract

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for the Si VII configurations 2s²2p⁴, 2s2p⁵, 2p⁶, 2s²2p³3s, 2s²2p³3p, and 2s²2p³3d, giving rise to 86 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 15, 30, 45, 60, and 75 ryd, 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, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10⁸-10¹⁴ cm^-3 assuming an electron temperature of logT_e(K)=5.8, corresponding to maximum ionic abundance of Si VII. Relative spectral line intensities are calculated. Proton excitation rates between the lowest three levels have been included in the statistical equilibrium equations. The predicted Si VII line intensities are compared with Solar EUV Rocket Telescope and Spectrograph (SERTS) observations in NOAA Active Region 5464 and Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of the quiet Sun.