Atomic data from the IRON project^*

LXIV. Radiative transition rates and collision strengths for Ca II

¹ Institute for Astrophysics and Computational Sciences, Department of Physics, The Catholic University of America, Washington, DC 20064, USA
² Exploration of the Universe Division, Code 667, NASA's Goddard Space Flight Center, Greenbelt, MD 20771, USA
³ Centro de Física, Instituto Venezolano de Investigaciones Científicas (IVIC), PO Box 21827, Caracas 1020A, Venezuela e-mail: bautista@kant.ivic.ve
⁴ Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK

Received: 8 February 2007
Accepted: 19 April 2007

Abstract

Aims.This work reports radiative transition rates and electron impact excitation rate coefficients for levels of the n = 3, 4, 5, 6, 7, 8 configurations of .

Methods.The radiative data were computed using the Thomas-Fermi-Dirac central potential method in the frozen core approximation and includes the polarization interaction between the valence electron and the core using a model potential. This method allows for configuration interactions (CI) and relativistic effects in the Breit-Pauli formalism. 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 with the most recent calculations and measurements for as well as a comparison between the core polarization results and the “unpolarized” values. We find that core polarization affects the computed lifetimes by up to 20%. Our results are in very close agreement with recent measurements for the lifetimes of metastable levels. The present 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 effective collision strengths for the resonance transitions are within ~11% from previous values derived from experimental measurements, but disagree with later computations using the distorted wave approximation.