Determining the size-dependent structure of ligand-free gold-cluster ions

Abstract

Ligand-free metal clusters can be prepared over a wide size range, but only in comparatively small amounts. Determining their size-dependent properties has therefore required the development of experimental methods that allow characterization of sample sizes comprising only a few thousand mass-selected particles under well-defined collisionfree conditions. In this review, we describe the application of these methods to the geometric structural determination of Au + n and Au − n with n = 3-20. Geometries were assigned by comparing experimental data, primarily from ion-mobility spectrometry and trapped ion electron diffraction, to structural models from quantum chemical calculations.

Far-IR Spectra of Small Neutral Gold Clusters in the Gas Phase

“…Most experimental investigations sensitive to structural details of gold clusters have been performed on charged species due to the possibility of easy mass separation and thereby size-selection. These studies give insight into an interesting structural evolution that does not have a direct parallel in other metals: the transition from 2-to 3-dimensional structures at comparably large sizes [7,8]. For the cationic clusters, the smallest cluster with a 3D geometry is Au8, while for the anions one finds the crossover at the 12-atom cluster with co-existing 2D and 3D structures.…”

“…Examples for such observations are the transition to insulator or even van-der-Waals bound clusters for certain metals [1,2], the optical properties of metal clusters or nano-particles embedded in glass [3,4], or the appearance of unprecedented chemical reactivity below a particular particle size. The discovery of high catalytic activity of gold nano-particles for low temperature CO oxidation [5] likewise has triggered many investigations of the physical and chemical properties of gas-phase gold clusters including their structures [6][7][8][9]. Most experimental investigations sensitive to structural details of gold clusters have been performed on charged species due to the possibility of easy mass separation and thereby size-selection.…”

Copper doping of small gold cluster cations: Influence on geometric and electronic structure

“…2 The remarkable large F Ar for Au 10 + , Au 11 + , and Au 15 + can most likely be attributed to almost planar faces of the Au 10 + quasi-tetrahedral structure, the fairly open prismatic structure of Au 11 + , 2, 41 and the layered structure of Au 15 + . 42 The pronounced odd-even oscillation of F Ar at small cluster sizes stays elusive. These odd-even variations might be a consequence of differences in the interaction between the Ar atom and the dipole moment of the Au atoms in the cluster.…”

Structures of small bismuth cluster cations

“…Note that in all comparative IMS and TIED studies performed so far on metal clusters we have observed no indication for metastable species. [36][37][38] One possible explanation for these findings is that isomer II is lost before the structure dependent measurement is taken, i.e., during injection into the drift cell in IMS or during trapping in the TIED experiment. In both cases a fraction of the lab frame kinetic energy (∼300 eV IMS, ∼25 eV TIED) is converted (via collisions with helium) into internal excitation of the cluster.…”