Investigation of the B1Î state in NaCs by polarisation labelling spectroscopy

► The B1Π ← X1Σ+ band system of NaCs observed. ► The last observed level in the B state located 7.6 cm−1 below the atomic asymptote. ► Potential energy curve of the B state determined between 2.4 and 24.8 Å. ► The existing photoassociation spectra of NaCs partially assigned.