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Polynuclear species of zirconium in acidic aqueous solution are investigated by combining X-ray absorption spectroscopy (XAFS) and nanoelectrospray mass spectrometry (ESI-MS). Species distributions are measured between pHC 0 and pHC 3 for [Zr]=1.5-10 mM. While the monomer remains a minor species, with increasing pH the degree of polymerization increases and the formation of tetramers, pentamers, octamers, and larger polymers is observed. The high resolution of the mass spectrometer permits the unambiguous determination of polynuclear zirconium hydroxide complexes by means of their isotopic patterns. The relative abundances of mononuclear and polynuclear species present simultaneously in solution are measured, even if one of the species contributes only 0.1% of the Zr concentration. For the first time it has been directly observed that the hydrolysis of polynuclear Zr species is a continuous process which leads to charge compensation through the sequential substitution of water molecules by hydroxide ligands until doubly charged polymers dominate at conditions (H+ and Zr concentrations) close to the solubility of Zr(OH)4(am). The invasiveness of the electrospray process was minimized by using very mild declustering conditions, leaving the polynuclear species within a solvent shell of approximately 20 water molecules.

Millimeter wave spectra of the alkaline earth metal oxides: BaO, SrO, and CaOMass spectra of metal-rich, singly and doubly ionized Ban Ox clusters are characterized by high peak intensities for n = 13, 19,23,26,29,32, and 35 independent ofthe number of oxygen atoms (x = 1,2,3,4). These values are identical to the magic numbers found for Ar clusters. The mass spectra of Can ° show a similar behavior. Mass spectra of stoichiometric, doubly ionized [Ca(CaO)n] ++ clusters are characterized by low peak intensities for n = 14, 24, 32, 38, 40, 50, and 64. These values correspond to unstable clusters formed by the addition of one Ca atom or one CaO molecule to a closed rectangular block of atoms with rock salt structure.

Abstract. Intensity anomalies (magic numbers) have been observed in the mass spectra of sodium clusters containing up to 22000 atoms. For small clusters (Na,, n ~< 1500) the anomalies appear to be due to the filling of electronic shells (groups of subshells having the same energy). The shells can be characterized rather well by a pseudoquantum-number, indicating the possible existence of a symmetry higher than spherical. The mass spectra of larger clusters (1500 ~ n ~< 22000) are well explained by the completion of icosahedral or cuboctahedral shells of atoms. The fact that the two types of shells (electron and atom) occur in distinct and non-overlapping size intervals might indicate the existence of a "liquid" to "solid" transition in going from small to large clusters.