Electron impact excitation of forbidden transitions in Si XI

Abstract
The excitation thresholds and oscillator strengths for the twelve lowest states of Si IX have been calculated using configuration interaction wavefunctions. The length and velocity values of the oscillator strengths agree closely with each other and the agreement between calculated and experimentally observed excitation threshold is better than 3%. These wavefunctions have been used in the R-matrix program to calculate the collision strengths below 10 Ryd for electron impact excitation of 52 forbidden transitions among the states having configurations 1s22s22p2, 1s22s2p3 and 1s22p4. The collision strengths exhibit a complex pattern of resonances in the entire energy range for almost all the transitions. These are averaged over a Maxwellian distribution of electron energies in a wide temperature range of 5000-250000K suitable for astrophysical applications. These are the first reported results in the literature for these transitions and are believed to be accurate to within 10% below 10000K.

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