(X)1 1Σ+ state of LiNa studied by Fourier-transform spectroscopy

Laser-induced fluorescence to the electronic ground state (X)1¹Σ⁺ of LiNa has been recorded by a Fourier-transform spectrometer. Optical excitations of the LiNa molecules into the (A)2¹Σ⁺ state were performed with different dye lasers. The spectra showed fluorescence progressions up to v^''=44 of the singlet ground state covering 99.9% of the potential well. However, searches for fluorescence into the triplet ground state (a)1³Σ⁺ induced by spin-orbit coupling in the excited system (b)1³Π-(A)2¹Σ⁺ were not successful. The potential energy curve of the singlet ground state was determined by direct potential fits with a data set of about 8200 assigned lines using two distinct analytical potential representations. In addition, the isotopologue ⁶Li²³Na was studied for a possible need of Born-Oppenheimer corrections by simultaneous fits of both observed isotopologues from ⁶Li and ⁷Li. Finally, new data on Feshbach resonances from cold-atom experiments at Heidelberg were included for improving the potential description around the dissociation energy for both electronic states (X)1¹Σ⁺ and (a)1³Σ⁺ of the atom-pair ground-state asymptote.