Fourier-transform spectroscopy and relativistic electronic structure calculation on the c3Σ+ state of KCs

•673 experimental term values belonging to both e/f -components of the c3ΣΩ=1+ state of KCs were determined with about 0.01 cm−1 accuracy applying high resolution Fouriertransform spectroscopy.•High fidelity relativistic coupled cluster calculation on the electronic structure of the KCs low-lying states was performed.•Semi-empirical point-wise interatomic potential was reconstructed for the c3Σ1+ state.•Ω -doubling effect in the c3Σ1+ state was investigated.•Radiative properties of the c3Σ+ state were simulated for the lowest vibrational vc≤22 levels.