The spin-orbit coupling of the 61Σ+ and 43Π states in KCs: Observation and deperturbation

Energies of 1655 rovibrational levels of the mutually perturbed and states in KCs were measured in a series of experiments employing polarization labelling spectroscopy technique. The experimental term values of the complex in KCs were used in coupled-channels deperturbation analysis which took explicitly into account the spin-orbit coupling of the and states. The empirical deperturbation treatment was supported by ab initio electronic structure calculation of adiabatic potentials of the interacting states and of the corresponding spin-orbit coupling matrix element as a function of internuclear distance.