Multifragmentation of the Au(H2O)n≤10+ Cluster Ions by Collision with Helium

A beam of mass selected Au(H2O)n+ (n = 1−10) cluster ions has been generated using a source that couples laser evaporation, supersonic expansion, and tandem time-of-flight mass spectrometry. A collision-induced-dissociation (CID) experiment has been performed with helium at energies in the range of 0.2−3 eV. A maximum of four water molecules is lost by the clusters. The key point is the data analysis where the total (loss of at least one water molecule) and partial (loss of a specified number of water molecules) CID cross sections have been simulated using a model describing the energy transfer between helium and the cluster. This has allowed us to fit the experimental data and to give insight into the structure and energetic of the Au(H2O)n+ clusters, unraveling the existence of two kinds of isomers for these clusters, one with two water molecules coordinating the metal ion, tentatively assigned to (H2O)p(H2O)Au+(H2O)(H2O)n-p-2, and a more compact one with three (or more) coordinating water molecules. Mu...