Radiative transition rates and collision strengths for Si II^*

¹ Department of Physics, Western Michigan University, Kalamazoo, MI 49008-5222, USA e-mail: manuel.bautista@wmich.edu
² Astrophysique et Spectroscopie, Université de Mons-Hainaut, 7000 Mons, Belgium
³ IPNAS, B15 Sart Tilman, Université de Liège, 4000 Liège, Belgium
⁴ Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK
⁵ Department of Physics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA

Received: 25 August 2009
Accepted: 20 October 2009

Abstract

Aims. This work reports on radiative transition rates and electron impact excitation collision strengths for levels of the 3s²3p, 3s3p², 3s²4s, and 3s²3d configurations of .

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.