3 years ago

Thermal Analysis of Hydrated Gold Cluster Cations in the Gas Phase

Thermal Analysis of Hydrated Gold Cluster Cations in the Gas Phase
Fumitaka Mafuné, Toshiaki Nagata
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 binding energy of directly bound H2O decreases as the cluster size increases; this size dependence most likely originates from the changes in the charge density of the Aun+ core.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04119

DOI: 10.1021/acs.jpcc.7b04119

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