Structures of Neutral Gold Clusters
Recently, gold clusters have attracted much of attention, mainly due to the remarkable catalytic properties of small gold particles. Additionally, with growing size gold clusters undergo a fascinating structural evolution. However, most of the knowledge on their structures comes from studies on charged clusters and so far there have been no direct experimental probes for the geometries of neutral gold clusters in the gas phase.
We have now investigated the vibrational spectra of neutral gold clusters by means of photodissociation of their complexes with rare gas atoms. These experiments make use of the “Free Electron Laser for Infrared eXperiments“ (FELIX) as source of intense and tunable radiation in the far-infrared. Multiple photon dissociation spectra are recorded in the range of the structure-specific vibrational fundamentals of the gold clusters, i.e. their finger-print range. Photodissociation signals are obtained from as low as 47 cm-1 to about 220 cm-1.
For example, a two-dimensional structure for neutral Au7 and a pyramidal structure for neutral Au20 can be unambiguously assigned. The lowering of the symmetry when a corner-atom is cut from the tetrahedral Au20 cluster is directly reflected in the vibrational spectrum of Au19. These larger neutral gold clusters adopt structures very similar to the ones determined for the corresponding anionic species.
- in German and English from the Max-Planck-Gesellschaft
- another one in Dutch and English from Netherlands's Stichting voor Fundamenteel Onderzoek der Materie (FOM)
The structure of Au7 depends on its charge state. Adding electrons leads to more open geometries with lower average coordination. The structures of the ionic clusters have been determined by ion mobility spectrometry (P. Weis, Int. J. Mass Spectr. 245 (2005) 1.)
Experimental (blue) and calculated (green) IR spectra of neutral Au19 and Au20