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The changes in the mean-square charge radius (relative to 209Bi), magnetic dipole, and electric quadrupole moments of 187,188,189,191Bi were measured using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). A large staggering in radii was found in 187,188,189Big, manifested by a sharp radius increase for the ground state of 188Bi relative to the neighboring 187,189Big. A large isomer shift was also observed for 188Bim. Both effects happen at the same neutron number, N=105, where the shape staggering and a similar isomer shift were observed in the mercury isotopes. Experimental results are reproduced by mean-field calculations where the ground or isomeric states were identified by the blocked quasiparticle configuration compatible with the observed spin, parity, and magnetic moment. ispartof: Physical Review Letters vol:127 issue:9 ispartof: location:United States status: published

We report the value of the electric quadrupole moment of $^{209}\mathrm{Bi}$ extracted from the atomic data. For this, we performed electronic structure calculations for the ground $^{4}S_{3/2}^{o}$ and excited $^{2}P_{3/2}^{o}$ states of atomic Bi using the Dirac-Coulomb-Breit Hamiltonian and the Fock space coupled-cluster method with single, double, and full triple amplitudes for the three-particle Fock space sector. The value of the quadrupole moment of $^{209}\mathrm{Bi}, Q{(}^{209}\mathrm{Bi})=\ensuremath{-}418(6)$ mb, derived from the resulting electric field gradient values and available atomic hyperfine splittings is in excellent agreement with molecular data. Due to the availability of the hyperfine constants for unstable isotopes of Bi, current atomic calculation allows also to correct their quadrupole moments.

The electron affinity (EA) of superheavy element Og is calculated by the use of the relativistic Fock-space coupled cluster (FSCC) and configuration interaction methods. The FSCC cluster operator expansion included single, double, and triple excitations treated in a non-perturbative manner. The Gaunt and retardation electron-electron interactions are taken into account. Both methods yield the results that are in agreement with each other. The quantum electrodynamics correction to EA is evaluated using the model Lamb-shift operator approach. The electron affinity of Og is obtained to be 0.076(4) eV., 11 pages, 5 tables, 3 figures

The YbOH triatomic molecule can be efficiently used to measure the electron electric dipole moment, which violates time-reversal (T) and spatial parity (P) symmetries of fundamental interactions [I. Kozyryev, N.R. Hutzler, Phys. Rev. Lett. 119, 133002 (2017)]. We study another mechanism of the T,P-violation in the YbOH molecule - the electron-electron interaction mediated by the low-mass axiolike particle. For this, we calculate the molecular constant that characterizes this interaction and use it to estimate the expected magnitude of the effect to be measured. It is shown that this molecular constant has the same order of magnitude as the corresponding molecular constant corresponding to the axion-mediated electron-nucleus interaction. According to our estimation, an experiment on YbOH will allow one to set updated laboratory constraints on the CP-violating electron-axion coupling constants.

The Ti:Saphire laser operated within 13800 - 11800 cm − 1 range was used to excite the c 3 Σ + state of KCs molecule directly from the ground X 1 Σ + state. The laser-induced fluorescence (LIF) spectra of the c 3 Σ + → a 3 Σ + transition were recorded with Fourier-transform spectrometer within 8000 to 10000 cm − 1 range. Overall 673 rovibronic term values belonging to both e / f -components of the c 3 Σ + ( Ω = 1 ± ) state of 39 KCs, covering vibrational levels from v = 0 to about 45, and rotational levels J ∈ [ 11 , 149 ] were determined with the accuracy of about 0.01 cm − 1 ; among them 7 values for 41 KCs. The experimental term values with v ∈ [ 0 , 22 ] were involved in a direct point-wise potential reconstruction for the c 3 Σ + ( Ω = 1 ± ) state, which takes into account the Ω -doubling effect caused by the spin-rotational interaction with the nearby c 3 Σ + ( Ω = 0 − ) state. The analysis and interpretation were facilitated by the fully-relativistic coupled cluster calculation of the potential energy curves for the B 1 Π , c 3 Σ + , and b 3 Π states, as well as of spin-forbidden c − X and spin-allowed c − a transition dipole moments; radiative lifetimes and vibronic branching ratios were calculated. A comparison of relative intensity distributions measured in vibrational c → a LIF progressions with their theoretical counterparts unambiguously confirms the vibrational assignment suggested in [J. Szczepkowski, et al., JQSRT, 204, 133–137 (2018)].

Radium compounds have attracted recently considerable attention due to both development of experimental techniques for high-precision laser spectroscopy of molecules with short-lived nuclei and amenability of certain radium compounds for direct cooling with lasers. Currently, radium monofluoride (RaF) is one of the most studied molecules among the radium compounds, both theoretically and recently also experimentally. Complementary studies of further diatomic radium derivatives are highly desired to assess the influence of chemical substitution on diverse molecular parameters, especially on those connected with laser cooling, such as vibronic transition probabilities, and those related to violations of fundamental symmetries. In this article high-precision \emph{ab initio} studies of electronic and vibronic levels of diatomic radium monochloride (RaCl) are presented. Recently developed approaches for treating electronic correlation with Fock-space coupled cluster methods are applied for this purpose. Theoretical results are compared to an early experimental investigation by Lagerqvist and used to partially reassign the experimentally observed transitions and molecular electronic levels of RaCl. Effective constants of $\mathcal{P}$-odd hyperfine interaction $W_{\rm{a}}$ and $\mathcal{P,T}$-odd scalar-pseudoscalar nucleus-electron interaction $W_{\rm{s}}$ in the ground electronic state of RaCl are estimated within the framework of a quasirelativistic Zeroth-Order Regular Approximation approach and compared to parameters in RaF and RaOH., Comment: 18 pages, 2 figures, 5 tables

The spin-forbidden a 3 Π − X 1 Σ + , a ′ 3 Σ + − X 1 Σ + and spin-allowed A 1 Π − X 1 Σ + electronic transitions dipole moments of carbon monoxide have been ab initio studied in the framework of multi-reference Fock space coupled cluster method combined with the finite-field approach and the generalized relativistic pseudo-potential model for the effective introducing the relativity in all-electron correlation treatment. Radiative lifetimes, τ i ( v ′ , J ′ ) , of the upper i ∈ [ a 3 Π , A 1 Π ] states were evaluated as a function of vibrational, v ′ , and rotational, J ′ , quantum numbers. The τ a -values derived for the triplet a 3 Π 1 ( 0 , 1 ) and a 3 Π 2 ( 0 , 2 ) states at the highest level of computation were found to be 2.59 and 142 ms, which are near perfect agreement with their best experimental counterparts (J. J. Gilijamse, et al., J. Chem. Phys., 127, 221102 (2007)). The intercombination a − X , a ′ − X transition probabilities were numerically proved to be proportional to α 2 , where α = e 2 / ℏ c is the fine structure constant.

We observed the A 1 Σ + ∼ b 3 Π → a 3 Σ + / X 1 Σ + laser-induced fluorescence (LIF) of the RbCs molecule excited from the ground X 1 Σ + state by the Ti:Sapphire laser. The LIF spectra from the common perturbed levels of the singlet-triplet A ∼ b complex was recorded by the Fourier-transform (FT) spectrometer with the instrumental resolution of 0.03 cm − 1 . The relative intensity distribution in the rotationally resolved A ∼ b → a 3 Σ + ( v a ) / X 1 Σ + ( v X ) progressions was measured, and their branching ratio was found to be about of 1 ÷ 5 × 10 − 4 in the bound region of the a 3 Σ + and X 1 Σ + states. The experiment was complemented with the scalar- and full-relativistic calculations of the A / b − X / a transition dipole moments (TDMs) as functions of internuclear distance. The relative systematic error in the resulting ab initio TDM functions evaluated for the strong A − X transition was estimated as few percent in the energy region, where the experimental LIF intensities are relevant. The relative spectral sensitivity of the FT registration system, operated with the InGaAs diode detector and CaF beam-splitter, was calibrated in the range [6 500, 12 000] cm − 1 by a comparison of experimental intensities in the long A ∼ b → X(vX) LIF progressions of the K2 and KCs molecules with their theoretical counterparts evaluated using the ab initio A − X TDMs. Both experimental and theoretical transition probabilities can be employed to improve the stimulated Raman adiabatic passage process, a → A ∼ b → X, which is exploited for a laser assembling of ultracold RbCs molecules.