The Oblate Structure and Unexpected Resistance in Reactivity of Ag 15 + with O 2

Theoretical studies have been carried out to investigate the unusual reactivity of Ag15 + cations with oxygen. Our previous work has shown that the reactivity of free metal clusters with oxygen entails a spin excitation that causes reduced reactivity in clusters with filled electronic shells and large HOMO-LUMO gaps. Earlier experiments on Ag15 + have shown that the cluster exhibits remarkable resistance to reactivity with oxygen despite having a valence electron count that is not expected to result in a filled electronic shell within the spherical jellium model. It is shown that Ag15 + , Ag14, and Ag13 clusters with 14 valence electrons, all have oblate bilayer atomic structures that lead to a splitting of the superatomic Dshell in a manner analogous to crystal field splitting of d-states in transition metals. The importance of the oblate structure is demonstrated by showing a correlation between an oblate deformation coefficient and the HOMO-LUMO gap of the different structures of Ag15 + . The oblate deformation results in the splitting of the electronic subshells and leads to an unusually large HOMO-LUMO gap and the unusual resistance of the cationic species to oxidation.