Fine Structure Radiative Transitions in C Ii and C Iii Using the Breit–pauli R-Matrix Method

Abstract

Extensive sets of radiative transitions in C II and in C III are obtained using the relativistic Breit-Pauli R-matrix (BPRM) method. In comparison with other accurate methods that can be applied to relatively few transitions, the BPRM method enables calculations of a large number of transitions with comparable accuracy for most of them. The present work reports large-scale calculations for two important ions obtaining 127 and 206 bound fine structure energy levels, resulting in 1681 and 4202 dipole allowed and intercombination transitions for C II and C III, respectively. Detailed comparison of the BPRM results is made with those from experimental and theoretical studies, including the relativistic multiconfiguration Dirac-Fock method. INTRODUCTIONThe Breit-Pauli R-matrix (BPRM) method [1] is being used to calculate a large number of oscillator strengths (f -values) [2][3][4][5]. The first large scale application of the BPRM method for the radiative transitions in Fe XXIV and Fe XXV [2] showed very good agreement, within 10%, of the f -values with the most accurate theoretical calculations available. Most of the experimental and theoretical studies for oscillator strengths and transition probabilities (A-values) are focused on a few or a limited number of transitions, whereas various spectral diagnostic models and astrophysical applications, such as plasma opacities, require f -or A-values for a very large number of transitions. Systematic calculations for radiative processes were carried out for most astrophysically abundant atoms and ions under the Opacity Project (OP [6][7][8][9]). The datasets obtained under the OP are available electronically through a database, TOPbase [10]. The calculations under the OP were carried out in LS coupling and no relativistic effects were considered. However, fine structure transitions, rather than LS multiplets, are needed for spectral diagnostics in astrophysical and laboratory plasmas. The Breit-Pauli R-matrix method developed under the Iron Project (IP, [1]) includes relativistic effects in the Breit-Pauli approximation [1,11,12] for collisional processes. Recently, the method has been extended to enable close coupling calculations of oscillator strengths (i) including the relativistic effects and (ii) considering a large number of transitions.The present study investigates the relativistic and electron-electron correlation effects in transitions of two important light ions, C II and C III. These two ions are of particular interest in the diagnostics of a number of astrophysical objects such as in early type stars and nebulae as well as in laboratory plasmas. THEORYProvided here is a brief summary of the the basics of the Breit-Pauli R-matrix method. The method for radiative bound-bound and bound-free transitions is derived from atomic collision theory and the coupled channel or close coupling (CC) approximation [1,6]. The computational method is based on the powerful R-matrix formalism that enables efficient, accurate, and large-scale calculations of compound (bound and c...

Critically Evaluated Spectral Data for Singly Ionized Carbon (C ii)

“…As a result, they observed only three weak peaks corresponding to excitation from the 2s2p 2 4 P term, while the remaining 35 measured peaks were associated with absorption from the ground 2s 2 2p 2 P term. The identifications were assisted by their own extensive Cowan code calculations and by comparisons with the R-matrix calculations of Nahar (1995). Kjeldsen et al (1999Kjeldsen et al ( , 2001 reported observed spectral lines in the range between 25 and 51 nm and stated that the absolute uncertainty of the measured peak energies is 0.015 eV, which corresponds to an uncertainty of 0.008-0.31 nm in wavelength.…”