| Relativistic calculations for allowed and forbidden fine structure transitions in Fe XX |
| S.N. Nahar |
| Astronomy & Astrophysics, 2004, Vol.413, p 779 |
An extensive set of oscillator strengths (f), line strengths (S) and radiative decay rates (A) for dipole allowed, intercombination and forbidden
transitions in Fe XX is presented. Results include 1792 bound fine structure levels of total angular momenta J=1/2-19/2 of even and odd parities, with
2 <= n <= 10, 0 <= l <= 14, orbital angular momenta, 0 <= L <= 14, and total spin multiplicities 2S+1 = 2,4,6, yielding to about 3.8 × 10
allowed and 13,874 forbidden transitions in Fe XX. These results far exceed the available data in literature. The existing data compiled by the
National Institute for Standards and Technology (NIST) are available for little over one hundred transitions, and the previously calculated data under
the Opacity Project includes 75 590 LS multiplets. The present ab initio calculations are carried out in the close coupling approximation using the
relativistic Breit-Pauli R-matrix method for allowed and intercombination E1 transitions. The wavefunction expansion includes 20 fine structure levels
of configurations 2s
2p, 2s2p
, and 2p
of the core ion Fe XXI. Computed energy levels are identified spectroscopically using a newly developed
procedure based on quantum defects and channel contributions. All 55 observed levels have been identified and are in agreement to much less than 1with most of the calculated values. Coefficients for radiative decays for the forbidden E2, E3, M1 transitions are obtained through atomic structure
calculations including relativistic terms in the Breit-Pauli approximation using the code SUPERSTRUCTURE. The theoretical transition probabilities are
compared with available values, with varying degree of agreement.
Complete electronic files for energies (e.g. Tables 3a, 3b, 7) and transition probabilities (e.g. Tables 4, 5, 8) are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/779