Cesium dimer spectroscopy on helium droplets

Visible absorption spectra of cesium-doped helium nanodroplets between 14 500 and 17600cm−1 were probed by laser-induced fluorescence. A strong absorption band peaking around 16700cm−1 is identified as Cs2 1(a)Σu+3−3Σg+3 transition. A broad unstructured band near 17520cm−1 is assigned as the Cs2 1(X)Σg+1−2Σu+1 transition. Explanations of the observations are discussed on the basis of ab initio potential curves calculated by Spies and Meyer [(unpublished)]. All spectra have been modeled using narrow Frank-Condon windows around the equilibrium internuclear distance of the lowest singlet and triplet states. Many observed absorption peaks of smaller intensities could be identified, some of which may be due to transitions of cesium trimers formed on the droplets.