Radiative transition rates and collision strengths for si II

Abstract

Aims: This work reports on radiative transition rates and electron impact excitation collision strengths for levels of the 3s23p, 3s3p 2, 3s24s, and 3s23d configurations of Si II. Methods: The radiative data were computed using the Thomas-Fermi-Dirac-Amaldi central potential, but with the modifications introduced by Bautista (2008) that account for the effects of electron-electron interactions. We also introduce new schemes for the optimization of the variational parameters of the potential. Additional calculations were carried out with the Relativistic Hartree-Fock and the multiconfiguration Dirac-Fock Methods: Collision strengths in LS-coupling were calculated in the close coupling approximation with the R-matrix method. Then, fine structure collision strengths were obtained by means of the intermediate-coupling frame transformation (ICFT) method which accounts for spin-orbit coupling effects.Results: We present extensive comparisons between the results of different approximations and with the most recent calculations and experiments available in the literature. From these comparisons we derive a recommended set of gf-values and radiative transition rates with their corresponding estimated uncertainties. We also study the effects of different approximations in the representation of the target ion on the electron-impact collision strengths. Our most accurate set of collision strengths were integrated over a Maxwellian distribution of electron energies and the resulting effective collision strengths are given for a wide range of temperatures. Our results present significant differences from recent calculations with the B-spline non-orthogonal R-matrix method. We discuss the sources of the differences. © 2009 ESO.