Radiative transition rates and collision strengths for Si?II

摘要

Aims. This work reports on radiative transition rates and electron impact excitation collision strengths for levels of the 3s23p, 3s3p2, 3s24s, and 3s23dconfigurations ofSi II. Methods. The radiative data were computed using theThomas-Fermi-Dirac-Amaldi central potential, but with the modificationsintroduced by Bautista (2008) that account for the effects ofelectron-electron interactions. We also introduce new schemes for theoptimization of the variational parameters of the potential. Additionalcalculations were carried out with the Relativistic Hartree-Fock andthe multiconfiguration Dirac-Fock methods. Collision strengths inLS-coupling were calculated in the close coupling approximation withthe R-matrix method. Then, fine structure collision strengthswere obtained by means of the intermediate-coupling frametransformation (ICFT) method which accounts for spin-orbit couplingeffects. Results. We present extensive comparisons between the results ofdifferent approximations and with the most recent calculations andexperiments available in the literature. From these comparisons wederive a recommended set of gf-values and radiative transitionrates with their corresponding estimated uncertainties. We also studythe effects of different approximations in the representation of thetarget ion on the electron-impact collision strengths. Our mostaccurate set of collision strengths were integrated over a Maxwelliandistribution of electron energies and the resulting effective collisionstrengths are given for a wide range of temperatures. Our resultspresent significant differences from recent calculations with theB-spline non-orthogonal R-matrix method. We discuss the sources of the differences. Key words: atomic data - atomic processes - line: formation - quasars: absorption lines - Sun: abundances - ISM: atoms