Isomers of Anionic Gold Oxide Clusters, AunO2–, Investigated by Thermal Desorption Spectrometry

Anionic gold oxide clusters, AunO2– (n = 2–5), were prepared by sequential O atom transfer reactions from N2O to Aun–. Response of the clusters to heat was investigated by gas-phase thermal desorption spectrometry and was compared with the behavior of AunO2– prepared by the reaction of Aun– with O2. No desorption of O2 was observed from Au4O2– prepared with N2O until 1000 K, but O2 desorbed from Au4O2– prepared with O2 at 500 K, indicating the formation of structural isomers. Theoretical calculations show that the most stable form of Au4O2–, which contains dissociated O atoms, is produced by oxidation with N2O and that the third most stable form of Au4O2–, which contains molecular O2, is produced by oxidation with O2. The desorption energy of O2 from Au5O2–, in which O2 is dissociatively chemisorbed on Au5–, was estimated from the temperature dependence of the cluster signal intensities. The experimentally determined desorption energies were consistent with the values obtained by theoretical calculation.