STRUCTURES AND BONDING PROPERTIES OF CA-O CLUSTERS INFERRED FROM MASS-SPECTRAL ABUNDANCE PATTERNS

Calcium oxide clusters were produced by a gas aggregation technique and investigated using time-of-flight mass spectrometry. Depending on the source conditions, either singly or doubly charged clusters dominate the mass spectrum. Singly charged (CaO)nCa(m)+(m = 0-5) clusters are observed for higher flows of inert carrier gas, whereas primarily doubly charged (CaO)nCa2+ (n = 3-100) clusters are observed at lower flows. The mass spectral abundance patterns indicate that the clusters have cubic structures resembling pieces of the fcc lattice of solid CaO. The most stable structures appear to be cuboids, cuboids with a complete terrace, and cuboids which have one O atom vacancy for each excess metal atom in the cluster. The latter structures may be stabilized by the donation of electrons from excess metal atoms into the vacancies, creating defects similar to solid-state color centers, or by the formation of metal-metal bonds.