Chemical reaction cage effect

Cage effect, solvent, 169, 216, 227 Calvin cycle, 283 Character table, 36 Charge transfer complexes, 83 from metal to ligand, 269 interaction, 286 intramolecular transitions, 85 ligand to metal (CTLM), 269 mechanism. 182 transition, characteristics of, 85 transitions, to solvent, 86, 102, 276 Chemical lasers, 222 spectroscopy, 230 Chemiluminescence, 160, 265 reactions, 266... 

In order for two reactants A and B to react in a bimoiecuiar reaction, they need to be brought in the vicinity of each other. When dispersed in a fluid, this happens by diffusive motion, which is entirely different from the free motion in the gas phase. Once an encounter between two reactants takes place, they will usually stay together much longer than in a gas phase due to a cage effect of the surrounding fluid molecules. This allows for numerous exchanges of energy between reactants and fluid, and thereby for activation and deactivation of the reaction complex. A complicated interplay between diffusion rates and reaction rates may determine the overall reaction rate in a fluid. We shall study an example of how diffusive motion and chemical reactions are combined in a description of chemical reactions in solution. 

Structure and mechanism in photochemical reactions. The reactions of geminal radical pairs created in bulk polymers are presented by Chesta and Weiss in Chapter 13. Of the many possible chemical reactions for such pairs, they are organized here by polymer and reaction type, and the authors provide solid rationalizations for the observed product yields in terms of cage versus escape processes. Chapter 14 contains a summary of the editor s own work on acrylic polymer degradation in solution. Forbes and Lebedeva show TREPR spectra and simulations for many main-chain acrylic polymer radicals that cannot be observed by steady-state EPR methods. A discussion of conformational dynamics and solvent effects is also included. 

Secondly, it will be noted that quite a minor reaction pathway in Scheme VI leads to the CIDNP effects, since the cage product phenylbenzoate has a yield of only 4%. The major decomposition reaction (1) involving benzoyloxy/ben-zoyloxy pairs does not produce CIDNP effects. Therefore (3lDNP effects, while giving evidence of free radicals, do not indicate that free radicals are the only intermediates in a chemical reaction. 

In a second example the discrete time-reversible propagation scheme for mixed quantum-classical dynamics is applied to simulate the photoexcitation process of I2 immersed in a solid Ar matrix initiated by a femtosecond laser puls. This system serves as a prototypical model in experiment and theory for the understanding of photoinduced condensed phase chemical reactions and the accompanied phenomena like the cage effect and vibrational energy relaxation. It turns out that the energy transfer between the quantum manifolds as well as the transfer from the quantum system to the classical one (and back) can be very well described within the mixed mode frame outlined above. 

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