Thermal Analysis of Hydrated Gold Cluster Cations in the Gas Phase

Abstract

The binding forms and desorption processes of H2O molecules bound in hydrated gold clusters, Aun(H2O)m+ (n = 2–8, m = 1–4), were investigated by gas-phase thermal analyses under chemical equilibrium conditions and by quantum chemical calculations. The gas-phase clusters were prepared by the laser ablation of a gold target in the presence of water vapor and detected by mass spectrometry. Aun(H2O)m+ clusters were found to release H2O upon heating, eventually losing all H2O molecules to generate Aun+ at temperatures below 1000 K. In sufficiently concentrated H2O vapor, adsorption and desorption of H2O to/from a given cluster approached equilibrium during heating, and the temperature dependence of this equilibrium provided binding energies of H2O to Aun(H2O)m+. The experimental and computational results suggest two types of H2O binding forms, one in which the H2O molecules are directly bound to the Aun+ core and the other in which H2O molecules are bound to other H2O molecules through hydrogen bonding. The bi...