Electron-impact excitation of the 3s3p  ¹P^o state of Mg-like ions: S⁴⁺,  Ar⁶⁺ , and Ca⁸⁺

Electron-impact excitation of the 3s3p  ¹P^o state of Mg-like ions ( S⁴⁺,  Ar⁶⁺ , and Ca⁸⁺ ) from their ground state is studied theoretically using the R -matrix method with 31 target states. Results are reported in the range of low incident electron energies for the total and differential cross sections of this excitation process as well as for the polarization fraction and the Stokes parameters P₁,  P₂ , and P₃ of the photons emitted on the decay of the excited 3s3p  ¹P^o state to the ground state. The agreement between experiment and the present results is good. We obtain a polarization fraction of about 35% at low incident electron energies in these ions.