Observation of D(2)1Π∼(2)3Π∼(2)3Σ+ states in KCs by polarisation labelling spectroscopy technique. Modelling of the D(2)1Π ∼ (2)3Π1 system.

Abstract A first attempt towards analysis of three strongly interacting electronic states in KCs molecule, D(2)1Π, (2)3Π, and ( 2 ) 3 Σ + , is presented. In this attempt a two-channel model is built for the D(2)1Π ∼ (2)3Π1 system. Our description results in two sets of Dunham-type coefficients and effective coupling terms, which allow to reproduce 2008 experimental values of energy levels for both states with an accuracy 0.029 cm − 1 in the range of vibrational levels below v = 13 where no influence from the ( 2 ) 3 Σ + state is observed.