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 3s^23p, 3s3p^2, 3s^24s, and 3s^23d 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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2009
- DOI:
- 10.1051/0004-6361/200913179
- arXiv:
- arXiv:0910.5425
- Bibcode:
- 2009A&A...508.1527B
- Keywords:
-
- atomic data;
- atomic processes;
- line: formation;
- quasars: absorption lines;
- Sun: abundances;
- ISM: atoms;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 6 figures, 5 tables within text, 2 electronic tables