Determination of the C(3)1Σ+ state potential energy curve in KCs molecule based on polarisation labelling spectroscopy data

The C(3)1Σ+ state of KCs molecule was studied experimentally employing the polarisation labelling spectroscopy (PLS) technique. The experiment extended the prior knowledge of the state adding more than 40 vibrational levels to the previously existing data. A pointwise potential energy curve was constructed for the investigated state with the inverted perturbation approach (IPA) method, basing on experimentally determined energies of over 1300 rovibrational levels. [Display omitted] •The C1Σ+ ← X1Σ+ band system was observed in KCs molecule using polarisation labelling spectroscopy.•More than 40 newly observed vibrational levels supplemented the already existing data concerning the C1Σ+ state.•A pointwise potential energy curve of the C1Σ+ state was constructed basing on energies of more than 1300 rovibrational levels.•The experimental potential and molecular constants were compared with theoretical predictions.