2002MNRAS.331..389W

The ab initio R -matrix method is used to calculate effective collision strengths for electron-impact excitation of the sulphur-like ion Clii in the close-coupling approximation. All 10 astrophysically important fine-structure forbidden transitions within the 3s² 3p⁴ (formula), (formula), (formula) ground configuration levels are considered. The 12 lowest LS target states are included in the calculation. Effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of electron velocities.
Result. are presented for electron temperatures in the range logT (K)=3.3 to logT (K)=5.5, appropriate for astrophysical applications. These are the only effective collision strength data that are currently available.