First observation of the 31Π and 41Π states of NaLi molecule

Two previously unknown electronic states of NaLi molecule have been observed by polarisation labelling spectroscopy in the energy region of 29 900–34 100 cm−1 above the bottom of the molecular ground state potential well. The states are identified as 31Π(Na(3d) + Li(2s)) and 41Π(Na(4p) + Li(2s)). The Dunham coefficients are derived for both states and the potential energy curves constructed by the Rydberg–Klein–Rees method.