Relativistic coupled cluster calculations of spectroscopic and chemical properties for element 120

The coupled cluster calculations with accounting for relativistic effects to study spectroscopic and chemical properties of element 120 (E120) are performed. Similar calculations for Ba are also done and they are in a good agreement with the experimental data. Dissociation energies of diatomic X-H and X-Au molecules, where X=E120, Ba, are calculated; for E120 they are found to be $1.5\div2$ times smaller than those for Ba

Observation of the distribution of nuclear magnetization in a molecule

International audienceRapid progress in the experimental control and interrogation of molecules, combined with developments in precise calculations of their structure, are enabling new opportunities in the investigation of nuclear and particle physics phenomena. Molecules containing heavy, octupole-deformed nuclei such as radium are of particular interest for such studies, offering an enhanced sensitivity to the properties of fundamental particles and interactions. Here, we report precision laser spectroscopy measurements and theoretical calculations of the structure of the radioactive radium monofluoride molecule, $^{225}$Ra$^{19}$F. Our results allow fine details of the short-range electron-nucleus interaction to be revealed, indicating the high sensitivity of this molecule to the distribution of magnetization, currently a poorly constrained nuclear property, within the radium nucleus. These results provide a direct and stringent test of the description of the electronic wavefunction inside the nuclear volume, highlighting the suitability of these molecules to investigate subatomic phenomena

Observation of the distribution of nuclear magnetization in a molecule

Rapid progress in the experimental control and interrogation of molecules, combined with developments in precise calculations of their structure, are enabling new opportunities in the investigation of nuclear and particle physics phenomena. Molecules containing heavy, octupole-deformed nuclei such as radium are of particular interest for such studies, offering an enhanced sensitivity to the properties of fundamental particles and interactions. Here, we report precision laser spectroscopy measurements and theoretical calculations of the structure of the radioactive radium monofluoride molecule, $^{225}$Ra$^{19}$F. Our results allow fine details of the short-range electron-nucleus interaction to be revealed, indicating the high sensitivity of this molecule to the distribution of magnetization, currently a poorly constrained nuclear property, within the radium nucleus. These results provide a direct and stringent test of the description of the electronic wavefunction inside the nuclear volume, highlighting the suitability of these molecules to investigate subatomic phenomena

Radiative lifetime of the A 2Π1/2 state in RaF with relevance to laser cooling

International audienceThe radiative lifetime of the $A$$^2 \Pi_{1/2}$ (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state is of relevance to the laser cooling of RaF via the optically closed $A$$^2 \Pi_{1/2} \leftarrow X$$^2\Sigma_{1/2}$ transition, which is an advantageous aspect of the molecule for its promise as a probe for new physics. The radiative decay rate $\Gamma = 2.9(2)\times 10^7$ s$^{-1}$ is extracted using the lifetime, which determines the natural linewidth of 4.6(3) MHz and the maximum photon scattering rate of $4.1(3)\times 10^6$ s$^{-1}$ of the laser-cooling transition. RaF is thus found to have a comparable photon-scattering rate with other laser-cooled molecules, while thanks to its highly diagonal Franck-Condon matrix it is expected to scatter an order of magnitude more photons when using 3 cooling lasers before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the $8P_{3/2}$ state in Fr to be 83(3) ns, in agreement with literature

Radiative lifetime of the A 2Π1/2 state in RaF with relevance to laser cooling

The radiative lifetime of the $A$$^2 \Pi_{1/2}$ (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate $\Gamma = 2.86(8) \times 10^7$$s^{-1}$ are of relevance to the laser cooling of RaF via the optically closed $A$$^2 \Pi_{1/2} \leftarrow X$$^2\Sigma_{1/2}$ transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Thanks to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just 3 cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the $8P_{3/2}$ state in Fr to be 83(3) ns, in agreement with literature

Pinning down electron correlations in RaF via spectroscopy of excited states

International audienceWe report the spectroscopy of 11 electronic states in the radioactive molecule radium monofluoride (RaF). The observed excitation energies are compared with state-of-the-art relativistic Fock-space coupled cluster (FS-RCC) calculations, which achieve an agreement of >99.71% (within ~8 meV) for all states. High-order electron correlation and quantum electrodynamics corrections are found to be important at all energies. Establishing the accuracy of calculations is an important step towards high-precision studies of these molecules, which are proposed for sensitive searches of physics beyond the Standard Model

Pinning down electron correlations in RaF via spectroscopy of excited states

We report the spectroscopy of 11 electronic states in the radioactive molecule radium monofluoride (RaF). The observed excitation energies are compared with state-of-the-art relativistic Fock-space coupled cluster (FS-RCC) calculations, which achieve an agreement of >99.71% (within ~8 meV) for all states. High-order electron correlation and quantum electrodynamics corrections are found to be important at all energies. Establishing the accuracy of calculations is an important step towards high-precision studies of these molecules, which are proposed for sensitive searches of physics beyond the Standard Model

Deformation versus Sphericity in the Ground States of the Lightest Gold Isotopes

International audienceThe changes in mean-squared charge radii of neutron-deficient gold nuclei have been determined using the in-source, resonance-ionization laser spectroscopy technique, at the ISOLDE facility (CERN). From these new data, nuclear deformations are inferred, revealing a competition between deformed and spherical configurations. The isotopes Au180,181,182 are observed to possess well-deformed ground states and, when moving to lighter masses, a sudden transition to near-spherical shapes is seen in the extremely neutron-deficient nuclides, Au176,177,179. A case of shape coexistence and shape staggering is identified in Au178 which has a ground and isomeric state with different deformations. These new data reveal a pattern in ground-state deformation unique to the gold isotopes, whereby, when moving from the heavy to light masses, a plateau of well-deformed isotopes exists around the neutron midshell, flanked by near-spherical shapes in the heavier and lighter isotopes—a trend hitherto unseen elsewhere in the nuclear chart. The experimental charge radii are compared to those from Hartree-Fock-Bogoliubov calculations using the D1M Gogny interaction and configuration mixing between states of different deformation. The calculations are constrained by the known spins, parities, and magnetic moments of the ground states in gold nuclei and show a good agreement with the experimental results