Breit–Pauli energy levels belonging to 2p4, 2s2p5, 2p6, 2p33ℓ configurations and all E1 transitions among these levels in Mg V
Introduction
Mg V is an important ion in the oxygen-isoelectronic sequence. Its lines are detected in the planetary nebula NGC 7027 [1], [2], [3], [4] and in the wide spectral ranges from soft X-rays to ultraviolet regions. They are also expected to be seen in the solar and astrophysical plasmas. Only a few calculations are available for the atomic structure of Mg V. Fischer and Saha [5] presented multiconfiguration Dirac–Hartree–Fock (MCDHF) energy levels belonging to the ground configuration 2s22p4 (3P, 1D, 1S) and E2 and M1 transitions among these levels for some oxygen-like ions including Mg V. Tachiev and Fischer [6] later presented data for E1, E2, M1, M2 transitions from odd levels belonging to 2s2p5, 2s22p33s, and 2s22p33d configurations of Mg V. The MCHF collection of Fischer [7] also presents both ab initio and energy adjusted values for E1 transitions among all but one of the levels belonging to the above configurations and the even configuration 2s22p33p, although the level 2s23p3 (2Po)3d1D2 was missing in these tabulations. Recently, Bhatia et al. [8] reported a calculation of atomic structure and collisional data for Mg V. For the atomic structure part they used the SUPERSTRUCTURE code of Eissner [9] and for the scattering part they used the codes of Eissner and Seaton [10] and Eissner [11] based on the distorted wave approximation. In the present calculation we shall examine only their [8] atomic structure part. Bhatia et al. [8] compared their 6-, 9-, and 24-configuration calculated values of 86 fine-structure levels with the observed values as given by the NIST [12] database. The 9-configuration results were presented only for lowest 46 levels. It might be expected that the 24-configuration results would be more accurate than the two other sets. However, on many occasions, their 6-configuration energy levels show better agreement with the observed values. For example, their 6-configuration results 3P0,1,2 levels belonging to the configuration 2s22p3 (2P)3s are some 800 cm−1 lower than corresponding observed values whereas there 24-configuration results are about 14,000 cm−1 lower than corresponding observed values. Similar behavior is manifested for the levels of 2s22p3 (2P)3d3P configuration. For 2s22p3 (2P)3p3P the observed values are not available. For this case, too, their 24-configuration energy values differ by amounts similar to their 6-configuration results. Interestingly, their 6-configuration results for the 2p6 1S0 pushed the level at least six positions down. In short, their energy levels of the 6-configuration or 24-configuration cases show some erratic behavior and in such a case both atomic and scattering data could be in error. It is for this reason we wanted to investigate this ion using our superposition of configuration code CIV3.
Section snippets
Method of calculation
In the present superposition of configurations approach, the configuration interaction (CI) wavefunction in the intermediate coupling scheme is given bywhere Φi represents the configuration state functions (CSFs) of different Li and Si with a common J, ai is the expansion coefficient, and π is the parity of the wavefunction. The radial parts of the CSFs are expressed as an analytic sum of one-electron orbitals of the formwhere the basis functions are
Results and discussions
In Table 2 we compare our oscillator strengths in length (fL) and velocity (fV) gauges with the corresponding results of Fischer [7] and most recent calculations of Bhatia et al. [8], for transitions with one of the 2p4 levels as the lower level. The present results and those of Fischer [7] agree very well, with the possible exception of the transition. The oscillator strength of this transition is small, so that any cancellation or other CI effects play a more dominant
Conclusion
We have performed a large scale LSJ calculation involving 120,736 configurations for the 86 fine-structure levels belonging to 2p4, 2s2p5, 2p6, and 2p33ℓ configurations and atomic parameters associated with 1073 E1 transitions between these levels. Energy adjustment procedures (“fine-tuning”) were adopted to refine the ab initio CI mixing coefficients. The oscillator strengths, transition probabilities, and line strengths for almost all of these transitions agree very well with the MCDF
Note added to the proof
We found a recent compilation by Podobedova et al. [17] who reported oscillator strengths, transition probabilities, and line strengths for several ions of magnesium including Mg V. Twenty-two of these transitions are rated as “A” (within 3% accuracy). The source of these 22 transitions is the ab initio calculation of Tachiev and Fischer [6]. We have compared our results with all these transitions and found excellent agreement for all but the only A-rated intercombination transition 2p4 1D2 → 2p3(
Acknowledgment
This work is supported by the PPARC UK, through Rolling Grant PP/D00103X/1.
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DIVISION XII / COMMISSION 14 / WORKING GROUP ATOMIC DATA
2008, Proceedings of the International Astronomical Union