Pure long-range ion-pair Cs2 molecules

We performed absorption measurements in dense cesium vapor, around the Cs second principal series lines (6s→7p). Three satellite bands peaking at 454.3, 459.1 and 471.6 nm are found. New ab initio Cs2 potential curves calculated with the inclusion of the spin–orbit interaction are used for the identification and simulation of the observed satellite bands. The 454.3 and 459.1 nm satellite bands stem from avoided crossings of long-range ion-pair potential curves with long-range covalent potential curves associated with various asymptotes. Semiclassical spectral simulations of these ion-pair satellite bands show satisfactory agreement with measured spectra.