Abstract:The results of systematic XPS measurements of all alkali metal carbonates (Li, Na, K, Rb and Cs) are presented. The first set of experiments was performed with "as received" commercial carbonate powders under liquid nitrogen conditions using a precooling procedure. A second set of experiments was performed under similar experimental conditions after a preliminary grinding (mechanical activation) of the carbonates. In addition, Na2COa "1H20, NaHCOa and KHCOa powders were studied. It was found that sample pre-cooling allows distinction between hydrocarbonates and carbonate hydrates. Storage in air leads to formation of hydrocarbonates at the surface of Li2COa and Na2COa. This phenomenon being more pronounced in the former. In contrast, K2COa forms a hydrate with one H20 molecule. Rb2COa and Cs2COa have hydrocarbonates as well as hydrates at the surface and this is more pronounced for Cs2COa. Grinding of the carbonates results in the formation of hydrocarbonates at the surface, the tendency to do so was found to increase down the group IA, namely, K < Rb << Cs. For the most part, the hydrocarbonates formed were unstable in vacuum even under liquid nitrogen conditions. Chemical trends in C ls and O ls binding energies in carbonates and hydrocarbonates of the Group IA are discussed and related to the nature of the anion and alkali cation.

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ABSTRACT:The geometric structure and bonding in [Mo 6 S 8 (CN) 6 ] 6Ϫ cluster were studied on the basis of quantum chemical ab initio and DFT (B3LYP) calculations with different basis sets. The geometry parameters of the Mo 6 S 8 core are in good agreement with the available crystal structure data. The electron density in the inner part of the Mo 6 octahedron is almost constant (ϳ0.04 -0.06 e/au 3 ). There is also noticeable electron density on the edges and faces of the Mo 6 S 8 polyhedron. The model of the electronic structure of the cluster under consideration starts from the mobile electrons moving in the potential well of the spherical symmetry. The resulting states are classified according to orbital quantum number l (e.g., 1s, 1p, 1d, 1f). Subsequent crystal field splitting leads to observable consequence of the one electron states of the O h point group symmetry.

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