[en] Negative ions homologous to N⁻ are interesting systems, since there are several bound terms within the ground configuration. The forbidden transitions between them, often dominated by the magnetic dipole contributions, are affected by term mixing—a relativistic effect. When increasing the nuclear charge in the homologous sequence of negative ions, this effect increases. In this paper we use systematic multiconfiguration Dirac–Hartree–Fock calculations to study these effects and predict affinities, level splittings and transition rates between bound states of N⁻, P⁻, As⁻, Sb⁻ and Bi⁻. By monitoring the line strengths we are able to predict the deviation from the non-relativistic LS-coupled values for transitions between levels of the lowest ³P term. For Sb⁻ the ¹D term is also bound, and the prediction for the rates of its transition to the ³P-levels is a challenge for theory. For Bi⁻ less is known experimentally and we analyze its structure and the relativistic contributions to it. (paper)

[en] A comprehensive theoretical study of correlation effects on the fine-structure splitting within the ground configuration 3d"9 of the Co-like Hf"4"5"+, Ta"4"6"+, W"4"7"+, and Au"5"2"+ ions is performed by employing the multi-configuration Dirac–Hartree–Fock method in the active space approximation. It shows that the core-valence correlation with the inner-core 2p electron is more significant than with the outer 3p and 3s electrons, and the correlation with the 2s electron is also noticeable. The core–core correlation seems to be small and can be ignored. The calculated "2D_3_/_2_,_5_/_2 splitting energies agree with the recent electron-beam ion-trap measurements [Phys. Rev. A 83 032517 (2011), Eur. Phys. J. D 66 286 (2012)] to within the experimental uncertainties. (paper)

[en] It is normally assumed that induced transitions, by e.g. hyperfine, magnetic field or spin interaction, arise due to mixing in the upper levels. In this paper we discuss an example when mixing in the lower levels through an externally applied magnetic field gives rise to a magnetic field induced transition. We discuss the theory for such a transition and give an example from Fe X, which is relevant for the determination of the magnetic field of the solar corona. To make this possible, it is important to determine the energy difference between the 3p ⁴3d ⁴ D _5/2 and ⁴ D _7/2, which are accidentally very close in energy in Fe X. The splitting of these levels is expected to be around 3.5 cm⁻¹ whereas their excitation energies are about 388 709 cm⁻¹. We discuss how this fine structure can be determined, by observing transitions from levels that decay into this pair which have a longer wavelength than the resonance transition. Finally we discuss an experimental scenario based on an electron beam ion trap and a Fabry–Perot interferometer, to perform the measurement of this interval. (paper)

[en] For all involved in astronomy, the importance of monitoring and determining astrophysical magnetic-field strengths is clear. It is also a well-known fact that the corona magnetic fields play an important part in the origin of solar flares and the variations of space weather. However, after many years of solar corona studies, there is still no direct and continuous way to measure and monitor the solar magnetic-field strength. We present here a scheme that allows such a measurement, based on a careful study of an exotic class of atomic transitions, known as magnetic induced transitions, in Fe⁹⁺. In this contribution we present a first application of this methodology and determine a value of the coronal field strength using the spectroscopic data from Hinode.

[en] Energies, transition rates, line strengths and lifetimes have been computed for all levels of the 4p ⁶ and 4p ⁵4d configurations of W³⁸⁺ by using the multi-configuration Dirac–Hartree–Fock (MCDHF) method as well as relativistic many-body perturbation theory. We investigate systematically correlation, relativistic and quantum electro-dynamical (QED) effects of different properties, including excitation energies and transition rates. We demonstrate that it is important to include the core-valence correlation of rather deep subshells (including 3d and 3p) to reach close to spectroscopic accuracy for the transition energies. We also show that high-multipole transitions (E3, M2) are important for the lifetime of some metastable levels of 4p ⁵4d (${}^3{F}_3,{}^1{D}_2,{}^3{D}_2$). The present results are in good agreement with experiments and of considerably higher accuracy than those achieved in previous theoretical works. (paper)

[en] Highlights: • Energies, transition rates, and lifetimes for the lowest 150 levels of the $3s^{2}3p^3,$ $3s3p^4,$ $3s^{2}3p^{2}3d,$ $3s3p^{3}3d,$ $3p^5,$ and $3s^{2}3p3d^2$ configurations in P-like Ge XVIII are provided. • The MCDHF and MBPT methods are employed. • The most accurate and complete atomic data for Ge XVIII are provided. Using the multiconfiguration Dirac-Hartree-Fock (MCDHF) and the relativistic configuration interaction (RCI) methods, a consistent set of transition energies and radiative transition data for the lowest 150 states of the $3s^{2}3p^3,$ $3s3p^4,$ $3s^{2}3p^{2}3d,$ $3s3p^{3}3d,$ $3p^5,$ and $3s^{2}3p3d^2$ configurations in P-like Ge XVIII is provided. To assess the accuracy of the MCDHF transition energies, we have also performed calculations using the many-body perturbation theory (MBPT). Comparisons are made between the present MCDHF and MBPT data sets, as well as with other available experimental and theoretical values. The resulting accurate and consistent MCDHF data set will be useful for line identification and modeling purposes. These data can be considered as a benchmark for other calculations.

[en] Highlights: • Excitation energies and wavelengths of $n=3$ states of the W LVII–W LXII tungsten ions are systematically investigated. • Electron correlation, Breit interaction and QED corrections to the excitation energies are studied in detail. Atomic properties of $n=3$ states of the W${}^{56+}$ - W${}^{61+}$ ions are systematically investigated through two state-of-the-art methods, namely, the second-order many-body perturbation theory, and the multi-configuration Dirac–Hartree–Fock method combined with the relativistic configuration interaction approach. The contributions of valence-valence and core-valence electron correlations, the Breit interaction, the higher-order retardation correction beyond the Breit interaction through the transverse photon interaction, and the quantum electrodynamical corrections to the excitation energies are studied in detail. The excitation energies and wavelengths obtained with the two methods agree with each other within $\approx 0.01$%. The present results achieve spectroscopic accuracy and provide a benchmark test for various applications and other theoretical calculations of W${}^{56+}$ - W${}^{61+}$ ions. They will assist spectroscopists in their assignment and direct identification of observed lines in complex spectra.