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We conducted measurement and calculation to resolve the long-standing large discrepancy in the metastable state lifetime for the 88Sr atom between theoretical and experimental results. The present lifetime τ = 830 − 240 + 600 s, measured using the magneto-optical trap as a photon amplifier to detect the weak decay events, is approximately 60% larger than the previous experimental value τ = 520 − 140 + 310 s. By considering the electron correlation effects in the framework of the multiconfiguration Dirac–Hartree–Fock theory, we obtained a theoretical lifetime of 1079(54) s, which lies in the range of measurements with error bars. Furthermore, we considered the higher-order electron correlation and Breit interaction to control the uncertainty of the theoretical calculation. The significant improvement in the agreement between calculations and measurements is attributed to the updated blackbody radiation-induced decay rate.

Systematic calculations and assessments are performed for the magnetic dipole (M1) transition energies and rates between the F 5 / 2 , 7 / 2 o 2 levels in the ground configuration 4d104f along the Ag-like isoelectronic sequence with 62 ⩽ Z ⩽ 94 based on the second-order many-body perturbation theory implemented in the Flexible Atomic Code. The electron correlations, Breit interaction and quantum electrodynamics effects are taken into account in the present calculations. The accuracy and reliability of our results are evaluated through comprehensive comparisons with available measurements and other theoretical results. For transition energies, our results are in good agreement with the recent experimental data obtained from the electron beam ion traps within 0.18%. The maximum discrepancy between our results and those obtained with the large-scale multiconfiguration Dirac–Hartee–Fock calculations by Grumer et al. [Phys. Rev. A 89 062501 (2014)] is less than 0.13% along the isoelectronic sequence. Furthermore, the corresponding M1 transition rates are also reported. The present results can be used as the benchmark and useful for spectra simulation and diagnostics of astrophysical and fusion plasmas.

The 4s24p 2P3/2–2P1/2 magnetic dipole transition in Ga-like ions is interested in developing of high precise highly charged ion clock (Yu and Sahoo 2019 Phys. Rev. A 99 022513). In this work, we present direct observations of the transition in Mo11+ and Ru13+ ions at an electron beam ion trap. Internal and external calibration methods are used for determining the wavelength of the Mo11+ and Ru13+ lines, respectively. Both measurements reach precision levels of a few ppm. Compared with the available values, the current results significantly improve the experimental uncertainty.

The transition energies, E1 transitional oscillator strengths of the spin-allowed as well as the spin-forbidden and the corresponding transition rates, and complete M1, E2, M2 forbidden transition rates for 1s 2, 1s2s, and 1s2p states of He I, are investigated using the multi-configuration Dirac–Hartree–Fock method. In the subsequent relativistic configuration interaction computations, the Breit interaction and the QED effect are considered as perturbation, separately. Our transition energies, oscillator strengths, and transition rates are in good agreement with the experimental and other theoretical results. As a result, the QED effect is not important for helium atoms, however, the effect of the Breit interaction plays a significant role in the transition energies, the oscillator strengths and transition rates.

We present an experimental determination on the Lande g-factors for the 5s2 1S0 and 5s5p 3 P0 states in ultra-cold atomic systems, which is important for evaluating the Zeeman shift of the clock transition in the 87Sr optical lattice clock. The Zeeman shift of the 5s5p 3P0–5s2 1S0 forbidden transition is measured with the π-polarized and σ±-polarized interrogations at different magnetic field strengths. Moreover, in the g-factor measurement with the σ±-transition spectra, it is unnecessary to calibrate the external magnetic field. By this means, the ground state 5s2 1S0 g-factor for the 87Sr atom is −1.306(52)×10−4, which is the first experimental determination to the best of our knowledge, and the result matches very well with the theoretical estimation. The differential g-factor δg between the 5s5p 3P0 state and the 5s2 1S0 state of the 87Sr atoms is measured in the experiment as well, which are −7.67(36) × 10−5 with π-transition spectra and −7.72(43) × 10−5 with σ±-transition spectra, in good agreement with the previous report [Phys. Rev. A 76 (2007) 022510]. This work can also be used for determining the differential g-factor of the clock states for the optical clocks based on other atoms.

We calculated the magnetic dipole hyperfine interaction constants and the electric field gradients of $2p^53p~^2[3/2]_2$ and $2p^53s~^2[3/2]^o_2$ levels of Ne I by using the multiconfiguration Dirac-Hartree-Fock method. The electronic factors contributing to the isotope shifts were also estimated for the $\lambda = 614.5$ nm transition connecting these two states. Electron correlation and relativistic effects including the Breit interaction were investigated in details. Combining with recent measurements, we extracted the nuclear quadrupole moment values for $^{20}$Ne and $^{23}$Ne with a smaller uncertainty than the current available data. Isotope shifts in the $2p^53p~^2[3/2]_2 - 2p^53s~^2[3/2]^o_2$ transition based on the present calculated field- and mass-shift parameters are in good agreement with the experimental values. However, the field shifts in this transition are two or three orders of magnitude smaller than the mass shifts, making rather difficult to deduce changes in nuclear charge mean square radii. According to our theoretical predictions, we suggest to use instead transitions connecting levels arising from the $2p^53s$ configuration to the ground state, for which the normal mass shift and specific mass shift contributions counteract each other, producing relatively small mass shifts that are only one order of magnitude larger than relatively large field shifts, especially for the $2p^53s~^2[1/2]^o_1 - 2p^6~^1S_0$ transition.

Weak- and hyperfine-interaction-induced 1s2s 1S0 → 1s2 1S0 E1 transition rates for the isoelectronic sequence of He-like ions have been calculated using the multi-configuration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction methods. The results should be helpful for the future experimental investigations of parity non-conservation effects.

Unexpected transitions are induced by weaker interactions not included in the gross structure model of the ion under investigation. We discuss different examples of such decay channels, starting with relativistic spin-induced transitions. These represented an important field of study a few decades ago, and we illustrate how some challenging cases can be treated very accurately with todayʼs computational techniques, while close degeneracy sometimes still prevents ab initio methods from obtaining accurate results. For hyperfine induced transitions we review some recent results and discuss remaining challenges for experiment and theory. Finally, we discuss the newly opened field of accurate calculations for transitions induced by an external magnetic field and point to some examples of where these are accessible for experimental tests.

XXVII International Conference on Photonic, Electronic and Atomic Collisions, Lanzhou, China, 24-30 July, 2013.

The hyperfine structure constants for the ground 4s24p 2P°3/2 and lowest excited states 4s25s 2S1/2 of 71Ga are calculated using the GRASP2K package based on the multi-configuration Dirac-Hartree-Fock method. Furthermore, the magnetic dipole (μ) and the electric quadrupole (Q) moments of the Ga isotopes from 67Ga to 81Ga are derived.

Large-scale calculations have been performed using the GRASP2K package to accurately determine the lifetime of levels in 2p53s configuration of neutral neon. In particular, we calculated the hyperfine-induced transition rates from two metastable levels 3P20,0 to the ground state for odd Ne isotopes. It was found that hyperfine interactions drastically quench the lifetime of these two levels.

On the basis of previous work, the hyperfine-induced 3s3p P-3(2) -> 3s(2) S-1(0) E1 transition probabilities of Mg-like ions were further calculated using the GRASP2K package based on the multiconfiguration Dirac-Hartree-Fock method. The contribution to the lifetime of the P-3(2) level from the 3s3p P-3(2) -> 3s(2) S-1(0) hyperfine-induced E1, 3s3p P-3(2) -> 3s3p P-3(1) M1, 3s3p P-3(2) -> 3s(2) S-1(0) M2 and 3s3p P-3(2) -> 3s3p P-3(0,1) E2 transition was discussed in detail. It was found that hyperfine interaction has an obvious effect on the lifetime at the beginning of the Mg-like isoelectronic sequence.

Hyperfine quenching rates for 1s2s 1S0 → 1s2 1S0 M1 transition of He-like ions, 2s2p 3P0 → 3P2 → 2s2 1S0 E1 transition of Be-like ions and 3s3p 3P0 → 3s2 S0 E1 transition of Mg-like ions have been calculated from relativistic configuration interaction wavefunctions including the frequency independent Breit interaction and QED effects. The present study not only supply accurate theoretical values for developing atomic clocks, diagnosing low-density plasma, probing nuclear properties, exploring weak interaction beyond standard model, but also to analyze some characteristics in hyperfine induced transitions.

Hyperfine quenching rates of the 3s3p3P0 level in Mg-like ions were calculated using the GRASP2K package based on the multi-configuration Dirac–Hartree–Fock method. Valence and core-valence correlation effects were accounted for in a systematic way. Breit interactions and QED effects were included in the subsequent relativistic CI calculations. Calculated rates were compared with other theoretical values and with experiment, and a good agreement with the latest experimental value for the ion (Rosenband et al 2007 Phys. Rev. Lett. 98 220801) was found. Furthermore, we showed in detail the contributions from Breit interaction and QED effects to concerned physical properties. Finally, electronic data were presented in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine-induced decay rates to be estimated for any isotope along the isoelectronic sequence.