Effective collision strengths for fine-structure forbidden transitions among the 3s23p4 levels of Cl ii

The ab initio R -matrix method is used to calculate effective collision strengths for electron-impact excitation of the sulphur-like ion Cl  ii in the close-coupling approximation. All 10 astrophysically important fine-structure forbidden transitions within the 3s²3p⁴     ,     ,     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. Results are presented for electron temperatures in the range  log  T (K)=3.3  to  log  T (K)=5.5  , appropriate for astrophysical applications. These are the only effective collision strength data that are currently available.