Gas solids, rare

A few ab initio calculations are the main source of our current, very meagre knowledge of non-additive contributions to the short-range energy [91], It is unclear whether the short-range non-additivity is more or less important than the long-range, dispersion non-additivity in the rare-gas solids [28, 92],... 

Zirconium difluoride [7783-49-5], Zrp2, has been isolated in rare gas—solid matrices (1). Zrp2, prepared by Knudsen ceU techniques, is not commercially available. 

Studies of the energetics and dynamics of Cu2 and Ag2 in rare gas solids have also been completed (31,34). The absorption and fluorescence spectra are similarly indicative of strong guest-host interactions in the low lying states of Cu2 and Ag2 Rather than presenting the spectroscopic and photolytic details, a summary of the observed radiative relaxation processes of visible and uv excited Cu2 and Ag2 in rare gas solids is shown below ... 

The absorption and fluorescence spectra of Ag2 in rare gas solids are also clearly indicative of strong guest-host interactions involving the A1 and C1 Instates of Ag2 as summarized below ... 

M. Giihr, in Coherent Dynamics of Halogen Molecules in Rare Gas Solids, ed. by S. De Silvestri, G. Cerullo, G. Lanzani. Coherent Vibrational Dynamics (CRC, Boca Raton, 2007), p. 173... 

Khatri, R. Charlton, M., Sferlazzo, P., Lynn, K.G., Mills Jr., A.P. and Roellig, L.O. (1990). Improvement of rare-gas solid moderators by using conical... 

Merrison, J.P., Charlton, M., Deutch, B.I. and Jorgensen, L.V. (1992). Field assisted moderation by surface charging of rare gas solids. J. Phys. 

D.J. Wales et al., The Cambridge Cluster Database, 2007, http //www-wales.ch.cam. ac.uk/CCD.html. A. Cuccoli, A. Macchi, V. Tognetti, R. Vaia, Monte Carlo computations of the quantum kinetic energy of rare-gas solids, Phys. Rev. B 47 (1993) 14923. 

Keywords Rare-gas solids, Cryocrystals, Electronic excitations, Self-trapping, Frenkel... 

Rare-gas solids (RGS), or atomic cryocrystals, are the model systems in physics and chemistry of solids, and enormous amount of information about electronic excitations in RGS has been documented in several books [2-5]... 

Jephcoat, A. P. (1998) Rare gas solids in the Earth s deep interior. Nature, 393, 355-8. 

The MC and MD methods permitting the variation of the shape of the cell are best suited for the study of phase transitions in solids. These methods have been used to study phase transitions of a few solids in the last few years. Among these are monatomic solids such as rare gas solids, ionic solids, and molecular solids. There are, however, some inherent limitations in these methods. While certain transitions are readily investigated by these methods, others are more difficult. The b.c.c. to f.c.c. transformation of monatomic solids is an example of a transition that is readily observed (5, 7) (see Figs. 2 and 3). This transition has been observed as a function... 

In the past five years, the field of metal-zeolite chemistry has developed to the point where a number of metal atomic and small cluster guests have been synthesized and unequivocally characterized by spectroscopic and crystallographic techniques. The silver-zeolite A, X and Y systems in particular have yielded a wealth of valuable structural and site information pertaining to silver guests in the size range of one to six atoms (3). The spectroscopy of these silver-zeolites can therefore be probed in detail and compared with the corresponding data for silver atoms and silver clusters immobilized in weakly interacting rare gas solid supports (4). 

In the case of the Ag° isomer in solid Ar, the spectroscopic and photochemical results indicate the operation of an efficient Ag3 - Agj + Ag photodissociative-recombination process localized in the matrix cage.However>for the Ag3 isomer in solid Kr and Xe, the available data leans heavily in favour of a photoisomerization to the Ag° structural form within a deformable matrix cage. The observation of thermal and photolytic reversibility,amongst other things,argues in favour of a photoisomerization rather than a photodissociation or photoionization process for the Ag3 isomer in Kr and Xe matrices.These photoprocesses for Ag3 and Ag3 in rare gas solids are summerized in Scheme III. 

At this point we note that the overall form of the absorption, fluorescence emission and excitation profiles for Agx, Ag + and AgP+ for AgxNaX and AgxNaY is superficially reminiscent of those observed for Ag°, Ag2 0, and Ag3 ° entrapped in rare gas solids (4-10). However, a number of important differences are also apparent. These details are discussed for each silver guest as a necessary prelude to the subject of metal-support interactions. 

Ag° atoms isolated in the cubo-octahedral site of rare gas solids. The observation of multiple structure on the 2P 2S absorption and large red spectral shifts for the 2P - 2S emission of site I entrapped Ag° atoms, indicates that the guest-host interactions are markedly different for the 2S and 2P states and can be explained in terms of site I relaxation effects, using a vibronic coupling model similar to that described in detail for Ag° atom rare gas cage complexes (5). 

E) Support Interactions in the Spectroscopy and Photoprocesses of Ag,+ in Zeolite X and Y It is interesting to compare the spectroscopic properties of site I, I isolated Agz in ZY with those for Agz entrapped in rare-gas solids (6). In the latter one finds a strongly blue shifted gas to matrix X,... 

Illustration of the X and A-state potential energy curves for gaseous,rare gas solid,and zeolite Y isolated Ag and Ag (15). 

This relates to the complications associated with the existence of at least two structurally distinct forms of Ags° in rare gas solids and the likelihood of confusing optical transitions, which appear spectroscopically to be similar in origin but which likely correspond to excitations between entirely different electronic states. 

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