Cluster expanded solids

The cluster-expanded solids exhibit increased capacities for uptake of water, methanol and ethanol. Even better uptake results were obtained with cluster solids... 

Due to particles extrusion, crystal lattice deformation expands to the adjacent area, though the deformation strength reduces gradually (Figs. 10(a)-10(other hand, after impacting, the particle may retain to plow the surface for a short distance to exhaust the kinetic energy of the particle. As a result, parts of the free atoms break apart from the substrate and pile up as atom clusters before the particle. The observation is consistent with results of molecular dynamics simulation of the nanometric cutting of silicon [15] and collision of the nanoparticle with the solid surface [16]. 

Fig. 9.5. Negative-ion FAB spectrum of solid Csl. The monoisotopic [(Csl)nl] cluster ion series (cf. expanded view of m/z 2205.4) is well suited for calibrating a wide mass range.

Interest in the chemistry of transition metal clusters is expanding rapidly in various directions, as indicated by three recent books1-3 and a selection of recent review articles.4-6 The concept of a cluster is being broadened to signify a species with properties between a mononuclear complex and a bulk solid material, irrespective of direct metal-metal bonding. Thus, a cluster is a... 

Owing to their larger size, coordination solids incorporating cluster cores in place of individual metal centers can be expected to have an expanded framework structure. This is of particular interest for 3D solids, wherein the expansion could produce a highly porous framework with host-guest properties similar to those of zeolites. 

Photochemical behaviour of coordination compounds described in previous chapters results mainly from electronic interactions between the central metal atom or ion and ligands in the hrst coordination sphere. An increased size of molecular systems to clusters and nanosized crystals expands the possibility of photoinduced electron transfer between the discrete electronic states to excitation within bands. Furthermore, interactions of nanoparticles with molecules yield unique materials, combining structural versatility of molecular species with collective properties of solids. 

This narrative echoes the themes addressed in our recent review on the properties of uncommon solvent anions. We do not pretend to be comprehensive or inclusive, as the literature on electron solvation is vast and rapidly expanding. This increase is cnrrently driven by ultrafast laser spectroscopy studies of electron injection and relaxation dynamics (see Chap. 2), and by gas phase studies of anion clusters by photoelectron and IR spectroscopy. Despite the great importance of the solvated/ hydrated electron for radiation chemistry (as this species is a common reducing agent in radiolysis of liquids and solids), pulse radiolysis studies of solvated electrons are becoming less frequent perhaps due to the insufficient time resolution of the method (picoseconds) as compared to state-of-the-art laser studies (time resolution to 5 fs ). The welcome exceptions are the recent spectroscopic and kinetic studies of hydrated electrons in supercriticaF and supercooled water. As the theoretical models for high-temperature hydrated electrons and the reaction mechanisms for these species are still rmder debate, we will exclude such extreme conditions from this review. 

The Hg atom has a 6s closed electronic shell. It is isoelec-tronic with helium, and is therefore van der Waals bound in the diatomic molecule and in small clusters. For intermediate sized clusters the bands derived from the atomic 6s and 6p orbitals broaden as indicated in fig. 1, but a finite gap A remains until the full 6s band overlaps with the empty 6p band, giving bulk Hg its metallic character. This change in chemical binding has a strong influence, not only on the physical properties of mercury clusters, but also on the properties of expanded Hg, and on Hg layers on solid and liquid surfaces. For a rigid cluster the electronic states are discreet and not continuous as in fig. 1. Also the term band for a bundle of electronic states will be used repeatedly in this paper, although incipient band might be better. As the clusters discussed here are relatively hot, possibly liquid, any discreet structure will be broadened into some form of structured band . 

Mixed molecular clusters can be prepared by two different techniciues (i) by a co-expansion, where a mixture of the dopant with a rare gas is expanded into fhe vacuum, or (ii) by a pick-up procedure, in which case the neat rare gas clusters prepared by a supersonic expansion travel through a chamber with a dopant and a buffer gas. For solid systems one is thus able to prepare clusters with the dopants... 

The present chapter is devoted to the comparatively new and rapidly developing subject of clusters, a field intermediate between atomic physics, chemistry and solid state physics, in which concepts borrowed from nuclear physics have also proved very important. Although the field is new, it has expanded very rapidly, and there are many different aspects beyond the scope of the present book. We therefore confine our attention to (i) a general introduction and (ii) some aspects of cluster physics which are specifically connected with material already presented in the previous chapters. 

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