IONIZATION-POTENTIALS AND GEOMETRICAL STRUCTURE OF PURE AND OXYGENATED BARIUM CLUSTERS

In this article, we present results obtained on structures of small ba re and oxygenated barium clusters produced by the laser vaporization t echnique. Contrary to the very weak Ba-Ba binding (0.202 eV), the Ba-O binding is rather strong (5.8 eV). As a consequence, extremely small amounts of oxygen in the cluster source are sufficient to induce the n ucleation of oxygenated barium clusters. Surprisingly, at least for su bstoechiometric systems, BanOm clusters exhibit the same icosahedral s tructure as bare clusters do. Mass spectra seem to indicate that repla cing a barium atom with a strongly polar BaO molecule does not affect the geometrical structure of the cluster. This aspect is more easily u nderstandable if we assume that the oxygen atom takes place inside the structure of the Ba-n cluster without significant distortions. Ab-ini tio calculations have been undertaken in order to give a satisfactory account of this hypothesis.