X 1Σ+ and a 3Σ+ states of the atom pair K plus Cs studied by Fourier-transform spectroscopy

A comprehensive study of the X (1)Sigma(+) and a (3)Sigma(+) electronic states of the K and Cs atom pair is presented. Abundant spectroscopic data include 1937 transitions to the a (3)Sigma(+) state and 13 724 transitions to the X (1)Sigma(+) state for K-39 Cs-133 which were obtained by Fourier-transform spectroscopy. From these data potential energy curves were constructed simultaneously for both states X (1)Sigma(+) and a (3)Sigma(+) which are coupled by the hyperfine interaction. This allows us to accurately model the potential close to K(4s) + Cs(6s) atom-pair asymptote which is required to simulate cold collision processes. Dissociation energies of the X (1)Sigma(+) state as D-e(X) = 4069.208(40) cm(-1) and of the a (3)Sigma(+) state as D-e(a) = 267.141(20) cm(-1) were determined. Scattering lengths are predicted for different KCs isotopologs and Feshbach resonances were calculated for magnetic fields up to 1000 G.