Atomic data from the Iron Project XLV. Relativistic transition probabilities for carbon-like Ar XIII and Fe XXI using Breit-Pauli R-matrix method

The Breit-Pauli R-matrix method developed under the Iron Project has been used to obtain exten- sive sets of oscillator strengths and transition probabil- ities for dipole allowed and intercombination ne struc- ture transitions in carbon like ions, Ar XIII and Fe XXI. The complete set consists of 1274 ne structure bound energy levels and 198 259 oscillator strengths for Ar XIII, and 1611 bound levels and 300 079 oscillator strengths for Fe XXI. These correspond to levels of total angular mo- menta of 0 J 7 of even and odd parities formed from total spin of 2S + 1 = 5, 3, 1, and orbital angular mo- menta 0 L 9 with n 10, 0 l 9f or each ion. The relativistic eects are included in the Breit-Pauli ap- proximation. The close coupling wavefunction expansion for each ion is represented by the lowest 15 ne struc- ture levels of target congurations, 2s 2 2p, 2s2p 2 and 2p 3 . The energy levels are identied spectroscopically using a newly developed identication procedure. The procedure also makes a correspondence between the ne structure energy levels and LS terms. This provides the check for completeness of the calculated levels. Comparison is made of the present energies and the f-values with the avail- able observed and theoretical values. Present transition probabilities agree very well with the relativistic atomic structure calculations of Mendoza et al. for the intercom- bination transitions, 2s2p 3 ( 5 S o) 2s 2 2p 2 ( 3 P1;2; 1 D2). This further indicates that the importance of the neglected Breit interaction decreases with ion charge and constrains the uncertainty in the present calculations to within 15% even for the weak transitions.