Linear gold clusters

As an additional point, the f-factors calculated for the four sites of Aujj [25], as well as those for several smaller and larger magic-number and non-magic number cuboctahedra, for most of which no real examples of gold cluster compounds exist, exhibit a linear dependence on the coordination number of each site. Several of these are shown in Fig. 5. Thus, the coordination numbers of... 

For each cluster size, the few lowest energy equilibrium isomers with molecular adsorption (MA) and two atoms adsorption (TAA) complexes are represented in Fig 8. Most of these structures are planar or near planar. For 4c, 5b, and 5d, only an O atom is not in the plane. Two atom adsorption leads to major structural changes in the gold cluster, particularly for n>5. For example, in the structures 5a, 6a, and 7a, a gold atom breaks the bonds to other Au atoms to form a highly stable linear O-Au-0 unit which bind each 0 atom to one of the remaining Au atoms. On the other hand, molecular adsorption induces only a modest relaxation in the host cluster, and the O2 molecule is attached on top of a Au atom preferably to the bridge position between two Au atoms. 

Figure 8 Non-linear optical effects. Scheme for the formation of two types of scattering centres at increasing fluences ofa laser pulse used to excite gold clusters. High fluence vaporized and expanded metal clusters limit light transmission Immediately after the pulse and are replaced, after energy transfer to the solvent, by solvent bubbles acting as secondary scattering centres. Medium fluence only solvent bubblesare formed. Low fluence. light transmission depends linearly on the Intensity.

The Haruta s discovery that nanosized gold particales adsorbed on metal-oxide powders facilitate a wide class of reactions under near-ambient conditions has attracted a worldwide interest [1]. It is known that gold is very inert in bulk phase. However, small gold clusters possess high reactivity in selective methane and alkenes oxidation and hydrogenation of linear alkenes [2]. So, gold nanoparticles have been found to be active catalysts for many reactions of industrial and environmental interest. 

In analogy to this study, the above mentioned study of the influence of the dimensionality on the absorption spectra of small gold clusters " showed— in addition to the features discussed above that the photoabsorption spectra carries relevant structural information. This can be easily seen in Fig. 3, where the spectra of linear chains and two-dimensional clusters of the same size show different features. Thus, optical spectroscopy can be used to distinguish between different cluster isomers and is therefore an important tool in structure determination. 

Fig. 51. Scanning electron microscope image of different stages of metalization of DNA. (a) Linear chain of separated palladium clusters connecting two gold contacts (b) magnification of (a) showing clusters with diameter > 40 nm (c) continuous coated DNA strand after one development step with a diameter larger than 40 nm. Reproduced with permission from Ref. (175). Copyright 2001, American Institute of Physics.

The T phonon term [25], corresponding to the center-of-mass motion of the clusters, can be safely extrapolated for temperatures below 2 K, and the linear term can be estimated from the known value of 7 for bulk gold [142] in the same temperature range. These two terms would be approximately equal for a temperature of about 40 mK. 

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