Study of excited electronic states of the 39KCs molecule correlated with the K(42S) + Cs(52D) asymptote: experiment and theory

Using the polarisation labelling spectroscopy, we performed the detailed analysis of the level structure of excited electronic states of the 39 KCs molecule in the excitation energy interval between 17500 cm−1 and 18600 cm−1 above the v = 0 level of the X1 + ground state. We prove that the observed states are strongly coupled by spin-orbit interaction above 18200 cm−1 , as manifested by numerous perturbations in the recorded spectra. The spectra are interpreted with the guidance of accurate electronic structure calculations on KCs, including potential energy curves, transition electric dipole moments, and represen- tation of the spin-orbit interaction with a quasi-diabatic effective Hamiltonian approach. The agreement between theory and experiment is found satisfactory and better than in case of previously available theo- retical data. This study confirms the accuracy of the polarisation labelling spectroscopy to analyse highly- excited electronic molecular states which present a dense level structure.