Atomic data from the Iron project LXIV: Radiative transition rates and collision strengths for Ca II

Meléndez, M. and Bautista, M.A. and Badnell, N.R. (2007) Atomic data from the Iron project LXIV: Radiative transition rates and collision strengths for Ca II. Astronomy and Astrophysics, 469. pp. 1203-1209. ISSN 0004-6361

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    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.