Atomic data for opacity calculations : XVIII . Photoionization and oscillator strengths of Si - like ions Sio , Sz + , AP ' , Ca 6 +

Abstraet. Photoionization cross sections, oscillator strengths and energy levels of the silicon-like ions. Sio, S2+, Ar4 and Ca6+ are calculated in the close coupling approximation using the R-matrix method. A large number of bound states with n S IO have been considered and oscillator strengths fortransitions among all thesestates and photoionization cross sections of all the bound stater are obtained. Partial photoionization cross sections of the ground state into various excited states of the residual ion are also obtained for each ion. Detailed comparisons have been made for the calculated energies, oscillator strengths and photoionization cross sections with available theoretical and experimental values. Whereas we findgoodagreement for theoscillator strengths with recent experimental data for Si" and S2+, there are very few previous data available for Ar" and Ca6+. The ground-state photoionization cmss sections for Sio agree well with the previous blosc coupling calculations, however the present R-matrix results show considerable differences from the background cross sections for Sio, S*+ and Ar4+ in the central Eeld approximations.