The RbSr²Σ⁺ground state investigatedviaspectroscopy of hot and ultracold molecules

Abstract

We report on spectroscopic studies of hot and ultracold RbSr molecules, and combine the results in an analysis that allows us to fit a potential energy curve (PEC) for the X(1) 2 Σ + ground state bridging the short-to-long-range domains. The ultracold RbSr molecules are created in a µK sample of Rb and Sr atoms and probed by two-colour photoassociation spectroscopy. The data yield the long-range dispersion coefficients C6 and C8, along with the total number of supported bound levels. The hot RbSr molecules are created in a 1000 K gas mixture of Rb and Sr in a heat-pipe oven and probed by thermoluminescence and laser-induced fluorescence spectroscopy. We compare the hot molecule data with spectra we simulated using previously published PECs determined by three different ab-initio theoretical methods. We identify several band heads corresponding to radiative decay from the B(2) 2 Σ + state to the deepest bound levels of X(1) 2 Σ + . We determine a mass-scaled high-precision model for X(1) 2 Σ + by fitting all data using a single fit procedure. The corresponding PEC is consistent with all data, thus spanning short-to-long internuclear distances and bridging an energy gap of about 75% of the potential well depth, still uncharted by any experiment. We benchmark previous ab-initio PECs against our results, and give the PEC fit parameters for both X(1) 2 Σ + and B(2) 2 Σ + states. As first outcomes of our analysis, we calculate the s-wave scattering properties for all stable isotopic combinations and corroborate the locations of Fano-Feshbach resonances between alkali Rb and closed-shell Sr atoms recently observed [Barbé et al., Nat. ]. These results and more generally our strategy should greatly contribute to the generation of ultracold alkali -alkaline-earth dimers, whose applications range from quantum simulation to state-controlled quantum chemistry.

Absolute numbering of asymptotic vibrational levels of diatomic molecules from cold-physics experiments

“…The highest vibrational level in 87 Rb 84 Sr and 87 Rb 87 Sr was predicted in Ref. [4] to be v = 66. Arbitrarily we labelled it with n = 3 and v = 65 with n = 2.…”

“…x in the formula equals to n + 0.5), obtaining a = 99.9306(4) MHz and x D = −0.018020 (4) (D e = 0 by definition). These parameters define locally the shape of the F (x, y) function as well as its inverse (5).…”

“…We took the experimental data from Table II of Ref. [4]. The highest vibrational level in 87 Rb 84 Sr and 87 Rb 87 Sr was predicted in Ref.…”

“…In a series of recently published papers, measurements of binding energies for the few last rovibrational levels in the ground electronic state were reported in RbYb [1], Yb 2 [2], CsYb [3] and RbSr [4] molecules. These studies were focused on the scattering properties of the corresponding ultra-cold atomic species, including the interatomic interaction potentials and scattering lengths.…”

“…The particular approach applied there, however, was not directly applicable for levels close to the dissociation limit. The experimental data reported in papers [1][2][3][4] motivated us to develop further the ideas of Ref. [5] and to check their validity for near asymptotic levels, thus offering an additional, purely algebraic tool to establish the true vibrational numbering in an electronic state.…”