Extensive and accurate datasets for radiative transitions in atomic species are required for studies of many astrophysical and laboratory plasma sources. These range from diagnostics of specific spectral features to the calculation of mean opacities of stellar and non-stellar astronomical objects. Previous calculations of large radiative datasets were carried out under the Opacity Project (hereafter OP; 1995, 1996), and have been archived in the electronically accessible database TOPbase by C. Mendoza and collaborators (Cunto et al. 1993). However, the non-relativistic OP calculations were in LS coupling and for dipole allowed transitions; fine structure transitions within the LS multiplets, and intercombination type transitions, were not considered. The OP datasets, primarily intended for the calculation of mean stellar opacities, are therefore of limited value for diagnostic purposes involving the analysis of observed transitions between fine structure levels. For light elements, and for low ionization stages, the OP datasets for a number of ions have been reprocessed to obtain fine structure oscillator strengths through purely algebraic transformation of line strengths (often utilising observed energies for improved accuracy). Among such works is the recent compilation of transition probabilities at the U.S. National Institute for Standards and Technology (NIST) for C, N, O ions (Wiese et al. 1996). Similarly, fine structure oscillator strengths have been obtained (using experimental level energies where available) for Fe II (IP.VII, Nahar 1995), Fe III (IP.XVII, Nahar and Pradhan 1996; this work also includes forbidden transitions), Si II (Nahar 1998), S II (Nahar 1997), and Si-ions Si I, S III, Ar V and Ca VII (Nahar 1993).
In addition to the non-relativistic fine structure oscillator strengths
derived from the OP data in LS coupling, several relativistic calculations
for forbidden (E2, M1) and intercombination transitions have been reported by
members of the Iron Project (IP.I, Hummer et al. 1993)
using the Breit-Pauli mode of the atomic structure code SUPERSTRUCTURE
(Eissner et al. 1974; Eissner 1991, 1998). The latter works include:
transition probabilities for forbidden
lines in Fe II (IP.XIX, Quinet et al. 1996), radiative rates for forbidden
transitions within the ground state configurations of ions in the
carbon and oxygen isoelectronic sequences (IP.XXII, Galavis et al. 1997),
transitions within the n=2 complex in ions of the boron isoelectronic
sequence (IP.XXIX, Galavis et al. 1998), and intercombination transitions in the
carbon isoelectronic sequence (IP.XXXIII, Mendoza et al. 1998).
A complete list and abstracts of IP papers can be found at
http://www.am.qub.uk/projects/iron/papers/.
Information on other radiative calculations by the authors and
collaborators, including photoionization and recombination of ions of
iron and other elements, can be found
at http://www-astronomy.ohio-state.edu/pradhan/.
The Iron Project work has so far concentrated primarily on collisional excitation of atomic ions including relativistic effects using the Breit-Pauli R-matrix (BPRM) method. However, analogous to the earlier LS coupling OP codes (Berrington et al. 1987), the BPRM atomic collision codes extended and developed for the IP, (Scott & Taylor 1982; Hummer et al. 1993; Berrington et al. 1995) can also be employed for radiative work. The present work represents the first such IP effort for systematic and large-scale calculation of transition probabilities, akin to the earlier OP work (Seaton et al. 1994). We describe the calculations, together with the nomenclature and formats used to identify the transitions and tabulate the data. The accuracy is ascertained from the overall level of agreement between the length and the velocity forms of the oscillator strengths, as well as by comparisons with previous calculations for more limited but accurate data.
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