Ionization energies of cesium and cesium oxide clusters

The vertical ionization potentials of 7 cesium and 86 oxidized cesium clusters were determined using the technique of photoionization mass spectrometry. The spectra were obtained using a tunablecw dye laser for clusters in a mass range 1 to 2024 amu. The vertical ionization potentials (IP) are presented as a function of size and composition. The ionization energies of cesium clusters, Cs_n, decrease with cluster size. Unusually low IP were observed for the enneamer, Cs₉, and for the cesium monoxide Cs₁₁ O. With increasing oxidation of the cesium metal clusters the IP decreases (suboxides) reaches a minimum at Cs(Cs₂O)_n and then increases (superoxides).