Clusters geometrical structure

Four of the most powerful methods presently applied to elucidate metal cluster geometric structure will be presented in the following. These are mass-selected negative ion photoelectron spectroscopy, infrared vibrational spectroscopy made possible by very recent advances in free electron laser (FEL) technology, gas-phase ion chromatography (ion mobility measurements), and rf-ion trap electron diffraction of stored mass-selected cluster ions. All methods include mass-selection techniques as discussed in the previous section and efficient ion detection schemes which are customary in current gas-phase ion chemistry and physics [71]. 

Winter B J, Parks E K and Riley S J 1991 Copper clusters the interplay between electronic and geometrical structure J. Chem. Rhys. 94 8618... 

The Au SR clusters isolated above are treated as conventional chemical compounds. We have been studying the basic properties (e.g., optical [15-18,22,34], photophysical [16,35], chiroptical, magnetic [42]) and geometric structures [43] of Au SG clusters (1-9) as a prototypical system. As an... 

Geometric structure of the bare metal clusters and the complexes formed by reaction are unknown and present a significant experimental challenge. Chemical studies are starting to imply something about the structure of the products and will be invaluable until more direct chemical physics probes are available. 

Boron clusters are the best understood clusters of the main group elements [7,8]. Today we are capable of explaining and predicting their geometric structures and... 

FIGURE 29,1 Geometric structures of B —B 3 clusters optimized at B3LYP/6-311 +G. ... 

An analysis of the correlation between the magnetic and geometrical structures of AunTM+ clusters, and a detailed study of the local magnetic moment of the TM impurity will be published elsewhere ... 

HDS catalysts have been characterized extensively with a wide variety of tools, and several extensive reviews of the subject have been presented (85,88-91). Substantial effort has been aimed at relating catalytic activity and selectivity to microscopic properties such as catalyst composition, electronic structure, and geometric structure. EXAFS investigations of working catalysts have provided information about the composition, average local coordination, and interatomic distances of atoms in the catalyst clusters. It has been concluded that the active phase under operating conditions is MoS2-like particles with a dimension of 10—20 A (92-94). 

The underlying motivation of the work presented in this paper is to provide a theoretical understanding of basic physical and chemical properties and processes of relevance in photoelectrochemical devices based on nanostructured transition metal oxides. In this context, fundamental problems concerning the binding of adsorbed molecules to complex surfaces, electron transfer between adsorbate and solid, effects of intercalated ions and defects on electronic and geometric structure, etc., must be addressed, as well as methodological aspects, such as efficiency and reliability of different computational schemes, cluster models versus periodic ones, etc.. 

Another aspect that is interesting to note concerns the dependence of the DFT gap on the orientation of the wire, indeed, for each wire size the following relation holds g[100] > g[lll] > Eg [110]. As has been pointed out in Ref. [121], this is related to the different geometrical structure of the wires in the [100], [111] and [110] directions. Indeed the [100], [111] wires appear as a collection of small clusters connected along the axis, while the [110] wires resemble a linear chain. So we expect that quantum confinement effects are much bigger in the [100], [111] wires, due to their quasi zero-dimensionality, with respect to the [110] wires. Further, the orientation anisotropy reduces with the wire width and it is expected to disappear for very large wires, where the band gap approaches that of the bulk material. 

We evaluated geometry relaxation in the lowest five excited electronic states and the Stokes shift values employing the Cs-symmetric Al(OH)4 model cluster. Geometric parameters for various electronic states were optimized at the CASSCF level and the resulting bond lengths, bond angles, and torsional angles are presented in Table 4.9. The optimized structures of the two lowest 12A" and 12A states with the hole localized on the O center are... 

The interpretation of the spectroscopic data on Ph-W and Ph-An clusters and cluster cations has been greatly facilitated by ab initio electronic structure calculations. Most of the calculations have been concerned with the electronic and geometric structures of the electronic ground state of the neutral clusters (see ref. [41] and references cited therein)... 

Fig. 33. Perspective views from the top-layer side (Panel a) and from the bottom-layer side (Panel b) of the representative, nearly-stoichiometric surface cluster V360 98- The geometric structure of the V205 (010)- surface cluster (see Fig. 26) involves the SINDOl optimized intra-layer bond lengths [28] and the crystallographic values of the bond angles and the inter-layer V-O bond length. The surface layer views of alternative perpendicular adsorptions of toluene on the bridging oxygen 0(2) from the top layer side (c) and from the bottom layer side (d), and two alternative parallel adsorptions (Panels e, f) on the bottom layer. In Panel d the same adsorbate-substrate separation as in Figs. 7a, 9 and 25e has been adopted, while in the remaining panels this separation has been increased by 1 A relative to those shown in Fig. 25...

Main-group clusters geometric and electronic structure... 

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