High accuracy theoretical investigations of CaF, SrF, and BaF and implications for laser-cooling

The NL-eEDM collaboration is building an experimental setup to search for the permanent electric dipole moment of the electron in a slow beam of cold barium fluoride molecules [Eur. Phys. J. D, 72, 197 (2018)]. Knowledge of molecular properties of BaF is thus needed to plan the measurements and in particular to determine an optimal laser-cooling scheme. Accurate and reliable theoretical predictions of these properties require incorporation of both high-order correlation and relativistic effects in the calculations. In this work theoretical investigations of the ground and the lowest excited states of BaF and its lighter homologues, CaF and SrF, are carried out in the framework of the relativistic Fock-space coupled cluster (FSCC) and multireference configuration interaction (MRCI) methods. Using the calculated molecular properties, we determine the Franck-Condon factors (FCFs) for the $A^2\Pi_{1/2} \rightarrow X^2\Sigma^{+}_{1/2}$ transition, which was successfully used for cooling CaF and SrF and is now considered for BaF. For all three species, the FCFs are found to be highly diagonal. Calculations are also performed for the $B^2\Sigma^{+}_{1/2} \rightarrow X^2\Sigma^{+}_{1/2}$ transition recently exploited for laser-cooling of CaF; it is shown that this transition is not suitable for laser-cooling of BaF, due to the non-diagonal nature of the FCFs in this system. Special attention is given to the properties of the $A'^2\Delta$ state, which in the case of BaF causes a leak channel, in contrast to CaF and SrF species where this state is energetically above the excited states used in laser-cooling. We also present the dipole moments of the ground and the excited states of the three molecules and the transition dipole moments (TDMs) between the different states.Comment: Minor changes; The following article has been submitted to the Journal of Chemical Physics. After it is published, it will be found at https://publishing.aip.org/resources/librarians/products/journals

Theoretical determination of the ionization potentials of CaF, SrF, and BaF

We present a comprehensive theoretical study of the ionization potentials of the MF (M=Ca, Sr, and Ba) molecules using the state-of-the-art relativistic coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)]. We have further corrected our results for higher-order excitations (up to full triples) and the QED self-energy and vacuum-polarization contributions. We have performed an extensive investigation of the effect of the various computational parameters on the calculated ionization potentials, which allowed us to assign realistic uncertainties to our predictions. For CaF and BaF, where precise experimental measurements are available, our predictions are in excellent agreement with the measured values. In the case of SrF, we provide a theoretical prediction of the ionization potential that deviates from the available experimental measurements, motivating further experimental investigations.</p

High accuracy theoretical investigations of CaF, SrF, and BaF and implications for laser-cooling

The NL-eEDM collaboration is building an experimental setup to search for the permanent electric dipole moment of the electron in a slow beam of cold barium fluoride molecules [NL-eEDM Collaboration, Eur. Phys. J. D 72, 197 (2018)]. Knowledge of the molecular properties of BaF is thus needed to plan the measurements and, in particular, to determine the optimal laser-cooling scheme. Accurate and reliable theoretical predictions of these properties require the incorporation of both high-order correlation and relativistic effects in the calculations. In this work, theoretical investigations of the ground and lowest excited states of BaF and its lighter homologs, CaF and SrF, are carried out in the framework of the relativistic Fock-space coupled cluster and multireference configuration interaction methods. Using the calculated molecular properties, we determine the Franck-Condon factors (FCFs) for the A2Π1/2→X2ς1/2+ transition, which was successfully used for cooling CaF and SrF and is now considered for BaF. For all three species, the FCFs are found to be highly diagonal. Calculations are also performed for the B2ς1/2+→X2ς1/2+ transition recently exploited for laser-cooling of CaF; it is shown that this transition is not suitable for laser-cooling of BaF, due to the nondiagonal nature of the FCFs in this system. Special attention is given to the properties of the A′2Δstate, which in the case of BaF causes a leak channel, in contrast to CaF and SrF species where this state is energetically above the excited states used in laser-cooling. We also present the dipole moments of the ground and excited states of the three molecules and the transition dipole moments (TDMs) between the different states. Finally, using the calculated FCFs and TDMs, we determine that the A2Π1/2→X2ς1/2+ transition is suitable for transverse cooling in BaF

Spin–orbit effects in optical spectra of gold–silver trimers

Cationic gold–silver trimers are ideal model systems for the evaluation of relativistic electronic structure theories. The closed-shell triangles allow one to test density functional and wavefunction-based methods in their prediction of optical properties, as dependent on composition and symmetry. Here we present the gas-phase optical spectra of AgNAu3−N+ (N = 0–3) clusters recorded by longitudinal photodissociation spectroscopy in the photon energy range 1.9–4.4 eV. The experimental data are compared to excited electronic state calculations in the framework of all-electron range-separated time-dependent density functional and equation-of-motion coupled cluster theory using two-component as well as the spin-free scalar relativistic theories. In particular, it is shown that for mixed trimers scalar-relativistic corrections are insufficient and a two-component approach becomes obligatory for a correct description of optical response properties including both spin–orbit coupling and charge-transfer effects