Fine structure effective collision strengths for the electron impact excitation of

Abstract

Electron impact excitation collision strengths are required for the analysis and interpretation of stellar observations. To date no evaluations exist for the ion. An 18-state R-matrix calculation has been performed. The target states are represented by configuration interaction wavefunctions and consist of the 18 lowest LS states, having configurations 3s23p3, 3s3p4 and 3s23p23d. These target states give rise to 39 fine structure levels and 741 possible transitions. The fine structure collision strengths were obtained by transforming to a jj-coupling scheme using the JAJOM program of Saraph and have been determined at a sufficiently fine energy mesh to delineate properly the resonance structure. The effective collision strengths are calculated by averaging the electron collision strengths over a Maxwellian distribution of velocities. The nonzero effective collision strengths for transitions between the fine structure levels are given for electron temperatures (Te) in the range log10 Te(K)=4.5–6.5. Data for transitions among the five fine structure levels arising from the 3s23p3 ground state configurations are considered in some detail in this paper. These calculations are the first evaluations of collision strengths and effective collision strengths for this ion.