Аннотация:Laser-induced fluorescence spectra of the transitions excited from the ground state of KCs molecule were recorded with Fourier-transform spectrometer IFS125-HR (Bruker) at the highest achievable spectral resolution of 0.0063 . Systematic study of the hyperfine structure (HFS) of the state for levels with and shows that the splitting monotonically increases with . The spectroscopic study was supported by ab initio calculations of the magnetic hyperfine interaction in and states. The discovered variation of the electronic matrix elements with the internuclear distance is in a good agreement with the observed -dependencies of the HFS. Overall set of available experimental data on the state was used to improve the potential energy curve particularly near a bottom, providing the refined dissociation energy =267.21(1) . The ab initio HFS matrix elements, combined with the empirical and PECs in the framework of the invented coupled-channel deperturbation model, reproduce the experimental term values of both ground states within 0.003 accuracy up to their common dissociation limit.