Laser cooling is a well-established technique for the creation of ensembles of ultracold neutral atoms or positive ions. This ability has opened many exciting new research fields over the past 40 years. However, no negatively charged ions have been directly laser cooled because a cycling transition is very rare in atomic anions. Efforts of more than a decade currently have ${\mathrm{La}}^{-}$ as the most promising candidate. We report on experimental and theoretical studies supporting ${\mathrm{Th}}^{-}$ as a new promising candidate for laser cooling. The measured and calculated electron affinities of Th are, respectively, $4901.35(48){\mathrm{cm}}^{-1}$ and $4832{\mathrm{cm}}^{-1}$, or 0.607 690(60) and 0.599 eV, almost a factor of 2 larger than the previous theoretical value of 0.368 eV. The ground state of ${\mathrm{Th}}^{-}$ is determined to be $6d^{3}7s^2{{}^{4}F}_{3/2}^e$ rather than $6d^{2}7s^{2}7p{{}^{4}G}_{5/2}^o$. The consequence of this is that there are several strong electric dipole transitions between the bound levels arising from configurations $6d^{3}7s^2$ and $6d^{2}7s^{2}7p$ in ${\mathrm{Th}}^{-}$. The potential laser-cooling transition is ${}^2{S}_{1/2}^o\leftrightarrow {{}^{4}F}_{3/2}^e$ with a wavelength of $2.6\mu \mathrm{m}$. The zero nuclear spin and hence lack of hyperfine structure in ${\mathrm{Th}}^{-}$ reduces the potential complications in laser cooling as encountered in ${\mathrm{La}}^{-}$, making ${\mathrm{Th}}^{-}$ a new and exciting candidate for laser cooling.

Combined relativistic configuration interaction and many-body perturbation calculations are performed for the 359 fine-structure levels of the 2s ² 2p ³, 2 s2p ⁴, 2p ⁵, 2s ² 2p ² 3l, 2 s2p ³ 3l, 2p ⁴ 3l, and 2s ² 2p ² 4l configurations in N-like ions from Ar xii to Zn xxiv. Complete and consistent data sets of energies, wavelengths, radiative rates, oscillator strengths, and line strengths for all possible electric dipole, magnetic dipole, electric quadrupole, and magnetic quadrupole transitions among the 359 levels are given for each ion. The present work significantly increases the amount of accurate data for ions in the nitrogen-like sequence, and the accuracy of the energy levels is high enough to enable the identification and interpretation of observed spectra involving the n = 3, 4 levels, for which experimental values are largely scarce. Meanwhile, the results should be of great help for modeling and diagnosing astrophysical and fusion plasmas.

Level energies, wavelengths, electric dipole, magnetic dipole, electric quadrupole, and magnetic quadrupole transition rates, oscillator strengths, and line strengths from combined relativistic configuration interaction and many-body perturbation calculations are reported for the 201 fine-structure states of the , , , , , , and configurations in all Ne-like ions between Cr xv and Kr xxvii. Calculated level energies and transition data are compared with experiments from the National Institute of Standards and Technology (NIST) and CHIANTI databases, and other recent benchmark calculations. The mean energy difference with the NIST experiments is only 0.05%. The present calculations significantly increase the amount of accurate spectroscopic data for the n > 3 states in a number of Ne-like ions of astrophysical interest. A complete data set should be helpful for analyzing new observations from solar and other astrophysical sources, and is also likely to be useful for modeling and diagnosing a variety of plasmas, including astronomical and fusion plasma.

The multiconfiguration Dirac–Hartree–Fock theory is used to calculate the $3d{}^9{}^{2}D_{3/2}\to {}^2{D}_{5/2}$ transition energy for Co-like ions with $Z=28–100$. We investigate how electron correlation, frequency-independent and -dependent Breit interactions, as well as QED corrections vary along the sequence. The well-understood frequency-independent Breit contribution has the largest contribution for all ions. Among the corrections to this, correlation decreases rapidly with $Z$, the frequency-dependent Breit contribution is important especially for high-$Z$ ions, and the self-energy contribution to the QED becomes the largest correction already for $Z>50$. We evaluate and compare results for the Self-energy in three different approximations, (i) the approach implemented in the grasp2k package, (ii) the method based on Welton's concept and (iii) a model operator approach recently developed by Shabaev and coworkers. Through comparison with experimental values, it seems that the third set of results have the best agreement with experiments, but the difference from experiments for high-$Z$ ions, is around 0.03%–0.04%, and therefore our results are outside the error bars of the experiments.

We have performed extensive multiconfiguration Dirac–Hartree–Fock calculations and second-order many-body perturbation calculations for F-like ions with Z = 24–30. Energy levels and transition rates for electric dipole (E1), electric-quadrupole (E2), electric-octupole (E3), magnetic dipole (M1), and magnetic-quadrupole (M2) transitions, as well as radiative lifetimes, are provided for the lowest 200 levels belonging to the , , , , , and configurations of each ion. The results from the two sets of calculations are in excellent agreement. Extensive comparisons are also made with other theoretical results and observed data from the CHIANTI and NIST databases. The present energies and wavelengths are believed to be accurate enough to aid line identifications involving the n = 3 and n = 4 configurations, for which observations are largely missing. The calculated wavelengths and transition data will be useful in the modeling and diagnostics of astrophysical and fusion plasmas.