Selecting clusters

Viggiano A A, Arnold S T and Morris R A 1998 Reactions of mass selected cluster ions in a thermal bath gas Int. Rev. Phys. Chem. 17 147-84... 

Figure 3.9. Transient C02 formation rates on Pd30 (a) and Pd8 (b) mass-selected clusters deposited on a MgO(lOO) film at different reaction temperatures [74]. In these experiments CO was dosed from the gas background while NO was dosed via a pulsed nozzle molecular beam source. The turnover frequencies (TOFs) calculated from the experiments displayed in (a) and (b) are displayed in the last panel (c). C02 formation starts at lower temperatures but reaches lower maximum rates on the larger cluster. (Figure provided by Professor Heiz and reproduced with permission from Elsevier, Copyright 2005).

Gas-phase metal oxide cluster cations have become increasingly interesting because of the possibility that a controlled reaction of size selected clusters might shed some light on condensed-phase catalysts. The possibility of producing small clusters in the condensed phase from deposition of gas-phase clusters has also been a driving force in the study of the reactivity of gas-phase ions. 

The deposition of mass and charge selected ions onto surfaces is underway but is in its infancy. How do the ions survive the collision with a surface This question has a myriad of answers depending on many variables and will have a future in investigative studies. A soft landing is now a possibility (280) and allows the potential spectroscopic investigation of trapped ions. So far no transition metal ions have been examined using this method but it is only a matter of time. Soft landings via inert gas matrices also have potential in the surface deposition of mass selected clusters. 

Experiments on Rh clusters5,106 reveal an oscillatory pattern of the average magnetic moment, with large values for N = 15, 16, and 19, and local minima for N = 13-14, 17-18, and 20. DFT calculations have been performed for selected clusters in that size range, usually assuming symmetric structures except for the smallest clusters.108-112 The conclusion reached by the various researchers is that the Rh clusters are magnetic. However, different experiments for the same cluster size show a lot of dispersion. 

Tada, M. and Iwasawa, Y. (2009) Model Systems in Catalysis From Single Crystals and Size Selected Clusters to Supported Enzyme Mimics (ed. R.M. Rioux), Springer, in press. 

Using photoelectron detection in a femtochemistry arrangement, we studied size-selected clusters of ionic systems, covering the transition from gas phase to condensed phase dynamics [6]. We investigated the solvent effect on Oj dissociation dynamics, and observed... 

Fig. 4.16 Main workflow used by HTSview. First a similarity matrix is computed based on Feature Tree similarity, Then the Feature Trees are clustered. For selected clusters MTree models are constructed. A QSAR matrix is computed based on the MTree as an align-...

We have discussed recent computational and spectroscopic results on the photoinduced hydrogen transfer and proton transfer chemistry in hydrogen-bonded chromophore-solvent clusters. The interplay of electronic spectroscopy of size-selected clusters and computational studies has led to a remarkably detailed and complete mechanistic picture... 

There is not yet, however, a definite detection of diffuse gamma-ray emission from galaxy clusters. While there is a preliminary evidence of gamma-ray emission from a dozen bright, radio-active clusters which host powerful radio galaxies and Blazars and are associated to unidentified EGRET sources (Co-lafrancesco 2002), many of the quiet, X-ray selected clusters only have upper limits for their emission at E > 100 MeV. 

Figure 24.4 Disciplinary distribution in the map of science of the references in the review publications for two selected clusters. Top Biosensing. Bottom Hybrid silica materials. See text and Figure 24.3 for details. (See color insert.)...

The Buck method is most useful for medium sized clusters, and in experiments that do not attempt detailed photochemical studies of the size selected clusters. High resolution spectroscopy of the selected clusters is impractical because the number per quantum state is small, due to the many occupied ro-vibrational... 

The kinetic method [42,43] is a relative method for thermochemical data determination which is based on measurement of the rates of competitive dissociations of mass-selected cluster ions. This method was introduced by Cooks [44] for proton affinity determination. Later, an extension of this method was proposed by Fenselau [45]. 

S. Fedrigo, T. L. Haslett, M. Moskovits, Direct Synthesis of Metal Cluster Complexes by Deposition of Mass-Selected Clusters with Ligand Iron with CO. J. Am. Chem. Soc. 1996, 118, 5083-5085. 

Caveats. Those familiar with cluster chemistry will mark the absence of cluster synthesis, framework dynamics and reactivity. Considerable information exists and these topics for selected cluster types are well developed in cluster reviews and edited volumes. However, our focus on electronic structure is deliberate. We wished to compare and contrast geometric and electronic structure across the large sweep of element composition and cluster size up to and including bulk materials. To keep the book of manageable size relative to a typical one-semester advanced course yet... 

Size selected clusters from molecular beams deposited on planar 2-dimensional (2-D) supports [ 1 ]... 

Figure 3. A schematic of the apparatus used to produce mass selected clusters.

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