Further Progress in Data Acquisition and Analysis on the A$^{1}\Sigma^{+}$ and b$^{3}\Pi$ States of NaK

This work is an extension of work reported at the 2014 DAMOP meeting, with additional data and a more detailed, extensive analysis. Current efforts to produce cold NaK molecules from cold atoms start with production of Feshbach resonances [1] followed by excitation to high-lying singlet or triplet states, and then one- or two-step possibly stimulated decay to $v$=0 of the $X$ ground state. Efficient use of these processes requires an accurate and detailed knowledge of NaK energy level structure. To meet requirements of current applications we have constructed a model based on direct fits of experimental term values to potentials and spin-orbit coupling elements. The model is now complemented by {\it ab initio} calculations of the spin-orbit functions.\\[4pt] [1] C.-H. Wu, M. Zwierlein et al., PRL {\bf 109}, 085301 (2012).