Nanoclusters of Silver and Gold Atoms

Abstract

Results of recent state-of-the-art quantum mechanical calculations of the formation energies in vacuum at 0 K of Ag_n-1 i and Ag_n⁺ clusters for 3≤n≤9 allow dissociation energies of Ag_n⁺ clusters to be calculated. The values over this range of sizes are inconsistent with the chemical and photochemical processes proposed in the photo-aggregation theory of latent image formation and chemical development. They are also in fundamental disagreement with zralues calculated by the classical molecules-in-clusters method. According to the quantum mechanical calculations, the Ag_n⁺ clusters could not exist with an effective lifetime in the positively charged state in the silver halide crystal or in an aqueous medium. The tetrahedron, as the most stable form for Ag₄⁺ and Ag₄⁺, is also excluded in favour of a planar rhombic form. This paper discusses experimental and theoretical studies of the structure of nanoclusters of Ag and Au atoms and a probable growth sequence from n = 2 to n = 13. The conclusion is reached that the n = 13 clusters may have an icosahedral structure with a central Ag or Ag_n⁺ ion, 12 Ag atoms near the vertices and covalent bonds along 6 edges forming Agr molecules. The calculations of dissociation energies of Ag_n⁺ clusters by quantum mechanical and classical methods are reviewed and the resolution of the inconsistencies between the results obtained with these methods is discussed.