Silver nuclear properties

The elements will be discussed in the order of increasing atomic number in the Periodic Table, i.e. nickel, zinc, technetium, ruthenium, silver, hafnium, tantalum, tungsten, rhem um, osmium, iridium, platinum, gold, and mercury. Full numerical data of the relevant nuclear properties are summarized, as for other elements, in Appendix 1. 

Radioactive metals can be used in radio-release methods for the determination of oxidizing agents in aqueous solutions. The decisive factors in the choice of the metal are the following the metal should not react with water, but should react with oxidizing agents to yield ions that do not form precipitates in aqueous media the metal should have a radionuclide with suitable nuclear properties. These conditions are met by thallium ( " TI) and silver ( ° Ag). 

It was also observed, in 1973, that the fast reduction of Cu ions by solvated electrons in liquid ammonia did not yield the metal and that, instead, molecular hydrogen was evolved [11]. These results were explained by assigning to the quasi-atomic state of the nascent metal, specific thermodynamical properties distinct from those of the bulk metal, which is stable under the same conditions. This concept implied that, as soon as formed, atoms and small clusters of a metal, even a noble metal, may exhibit much stronger reducing properties than the bulk metal, and may be spontaneously corroded by the solvent with simultaneous hydrogen evolution. It also implied that for a given metal the thermodynamics depended on the particle nuclearity (number of atoms reduced per particle), and it therefore provided a rationalized interpretation of other previous data [7,9,10]. Furthermore, experiments on the photoionization of silver atoms in solution demonstrated that their ionization potential was much lower than that of the bulk metal [12]. Moreover, it was shown that the redox potential of isolated silver atoms in water must... 

Cluster properties, mostly those that control electron transfer processes such as the redox potential in solution, are markedly dependent on their nuclearity. Therefore, clusters of the same metal may behave as electron donor or as electron acceptor, depending on their size. Pulse radiolysis associated with time-resolved optical absorption spectroscopy is used to generate isolated metal atoms and to observe transitorily the subsequent clusters of progressive nuclearity yielded by coalescence. Applied to silver clusters, the kinetic study of the competition of coalescence with reactions in the presence of added reactants of variable redox potential allows us to describe the autocatalytic processes of growth or corrosion of the clusters by electron transfer. The results provide the size dependence of the redox potential of some metal clusters. The influence of the environment (surfactant, ligand, or support) and the role of electron relay of metal clusters in electron transfer catalysis are discussed. 

The increase of the redox potential of a metal cluster in a solvent with its nuclearity is now well established 1-4). The difference between the single atom and the bulk metal potentials is large (more than 2 V, for example, in the case of silver (3)). The size dependence of the redox potential for metal clusters of intermediate nuclearity plays an important role in numerous processes, particularly electron transfer catalysis. Although some values are available for silver clusters (5, 6), the transition of the properties from clusters (mesoscopic phase) to bulk metal (macroscopic phase) is unknown except for the gas phase (7-9). 

The dependence of cluster potential on nuclearity was obtained by changing the reference potential in a series of redox monitors (Table 5). The redox potentials of hydrated silver clusters are seen to increase with n. The data in Fig. 11 indicate that, at least for the redox properties of silver clusters, the transition between the meso-... 

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