Origin of the Unusual Properties of Aun(BO2) Clusters

Abstract

We report the discovery of a new class of clusters consisting of Aun(BO2) that forms during the oxygenation of gold clusters when boron nitride is used as insulation in a pulsed-arc cluster ion source (PACIS). Photoelectron and mass spectroscopy of these clusters further revealed some remarkable properties: instead of the expected AunOmpeaks, the mass spectra contain intense peaks corresponding to Aun(BO2) composition. Some of the most predominant features of the electronic structure of the bare Au clusters, namely even–odd alternation in the electron affinity, are preserved in the Aun(BO2) species. Most importantly, Aun(BO2) [odd n] clusters possess unusually large electron affinity values for a closed-shell cluster, ranging from 2.8–3.5 eV. The open-shell Aun(BO2) [even n] clusters on the other hand, possess electron affinities exceeding that of F, the most electronegative element in the periodic table. Using calculations based on density functional theory, we trace the origin of these species to the unusual stability and high electron affinity of the BO2 moiety. The resulting bond formed between BO2 and Aunclusters preserves the geometric and electronic structure of the bare Aunclusters. The large electron affinity of these clusters is due to the delocalization of the extra electron over the Auncluster.