(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>X</mml:mi></mml:math>)1<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mn>1</mml:mn></mml:msup><mml:mspace width="-0.16em"/><mml:msup><mml:mi>Σ</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math>state of LiNa studied by Fourier-transform spectroscopy

Laser-induced fluorescence to the electronic ground state $(X){1}^{\phantom{\rule{0.16em}{0ex}}1}{\ensuremath{\Sigma}}^{+}$ of LiNa has been recorded by a Fourier-transform spectrometer. Optical excitations of the LiNa molecules into the $(A)2{}^{\phantom{\rule{0.16em}{0ex}}1}{\ensuremath{\Sigma}}^{+}$ state were performed with different dye lasers. The spectra showed fluorescence progressions up to ${v}^{\ensuremath{'}\ensuremath{'}}=44$ of the singlet ground state covering 99.9$%$ of the potential well. However, searches for fluorescence into the triplet ground state $(a)1{}^{\phantom{\rule{0.16em}{0ex}}3}{\ensuremath{\Sigma}}^{+}$ induced by spin-orbit coupling in the excited system $(b){1}^{\phantom{\rule{0.16em}{0ex}}3}\ensuremath{\Pi}$--$(A)2{}^{\phantom{\rule{0.16em}{0ex}}1}{\ensuremath{\Sigma}}^{+}$ 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 ${}^{6}\text{Li}{}^{23}\text{Na}$ was studied for a possible need of Born-Oppenheimer corrections by simultaneous fits of both observed isotopologues from ${}^{6}$Li and ${}^{7}$Li. 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 $(X)1{}^{\phantom{\rule{0.16em}{0ex}}1}{\ensuremath{\Sigma}}^{+}$ and $(a)1{}^{\phantom{\rule{0.16em}{0ex}}3}{\ensuremath{\Sigma}}^{+}$ of the atom-pair ground-state asymptote.