Cluster isolated chemical reactions

These examples are only a few demonstrations of the general effort to use cluster reactions as a bridge between isolated binary systems and bulk reactions. The cluster isolated chemical reaction (CICR) technique elaborated in Chapter 2 of this Part is an important advance in that direction. 

Hence there is no gas-phase experiment yet which fully encompasses all aspects of an electron-transfer reaction in solution. In solution, the solvent acts first as a polarization medium, which affects the energetics of direct transfers from the donor to the acceptor. It can also act as a transport medium for indirect electron transfers. The first aspect has been addressed in various cluster experiments [276]. The second aspect was addressed more recently by considering the femtosecond dynamics of iodide-(water) anion clusters, as reviewed below [277]. Finally, clusters present the advantage of isolating one reaction pair free from secondary collisions, except those, which are desired, with the solvent molecules (or atoms). The latter consideration motivated the cluster isolated chemical reaction (CICR) technique reviewed in Section 2.8.3. 

The cluster isolated chemical reaction (CICR) technique was developed in Saclay to permit quantitative studies of heterogeneous chemical processes at a microscopic level. The ultimate goal is to document the coupling between a reaction coordinate... 

The fate of the reaction product in cluster isolated chemical reactions... 

Mestdagh JM, Gaveau MA, Gee C, Sublemontier O, Visticot JP. 1997. Cluster isolated chemical reactions . Int. Rev. Phys. Chem. 16(2) 215-247. 

One interesting challenge that reactions in van der Waals and hydrogen-bonded clusters offer is the possibility of studying specifically how weak interactions or microsolvation bonds affect a chemical reaction or dissociation process. In that sense, theoretical studies of weakly bound clusters have proved to be useful in learning about the crossover in behavior from that of an isolated nonsolvated molecule in the gas phase to that for a molecule in a liquid or solid solvent. 

Another important zeolite-catalyzed chemical reaction is the decomposition of NO. Cu-exchanged zeolites, especially Cu-ZSM-5, have been shown to catalyze the decomposition of NO in the presence of hydrocarbons and excess oxygen. The increasing awareness of the detrimental effects of automobile exhaust has prompted several theoretical studies on the active site and reaction mechanism. ° Cu-ZSM-5 was described using an empirical force field and energy minimization to locate the copper ions in ZSM-5. Isolated copper atoms and copper clusters were found in the micropores, mostly associated with framework aluminium species. A cluster of two copper ions bridged via an OH species not part of the zeolite framework ( extra-framework ) was proposed as the active site. Quantum mechanical cluster calculations were carried out to study the elementary steps in the NO decomposition. A single T-site model was used to represent the zeolite framework. 

The chemical reduction of the higher Mo and W halides provides good yields of the octahedral clusters, but the mechanism is obscure. By contrast, chemical oxidation of zero-valent Mo and W leads to the bromo and iodo cluster species in poor yields but provides considerable insight into the formation of these cluster compounds. The reaction of the hexacarbonyls Mo(CO)6 or W(CO)6 with I2 at moderately low temperatures produces a mixture of metal halide phases (25, 16). In the reaction W(CO)6 with I2, lower nuclearity clusters have been isolated as reaction intermediates that lead to W6 species. The tri-, tetra-, and pentanuclear tungsten iodide species are obtained from W(CO)6 and I2 by varying reaction times and temperatures, and the... 

Cluster impact chemistry provides a new dynamical regime, hitherto not accessible to systematic exploration. High barrier chemical reactions can be studied under de facto isolated gas phase collsion conditions. On the other hand, ternary (and even higher order) encounters, which were of special interest to Bodenstein [24], can be explored. The unique features of the scheme are the high material and energy density conditions which can be established very rapidly, leading to super-heating (which has already been experimentally demonstrated [7]) on a time scale shorter than even typical intramolecular events. 

Even under matrix isolation conditions some chemical reactions occur. A large number of reactions with atoms (especially the alkalis) have been observed. Reactions between CO and Cu or Ni clusters have been studied by... 

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