Redistribution reactions particular systems

In this chapter we shall first outline the basic concepts of the various mechanisms for energy redistribution, followed by a very brief overview of collisional intennoleciilar energy transfer in chemical reaction systems. The main part of this chapter deals with true intramolecular energy transfer in polyatomic molecules, which is a topic of particular current importance. Stress is placed on basic ideas and concepts. It is not the aim of this chapter to review in detail the vast literature on this topic we refer to some of the key reviews and books [U, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, and 32] and the literature cited therein. These cover a variety of aspects of tire topic and fiirther, more detailed references will be given tliroiighoiit this review. We should mention here the energy transfer processes, which are of fiindamental importance but are beyond the scope of this review, such as electronic energy transfer by mechanisms of the Forster type [33, 34] and related processes. 

Equilibrium isotope-exchange reactions involve the redistribution of isotopes of an element among various species or compounds in a closed, well-mixed system at chemical equilibrium. At isotope equilibrium, the forward and backward reaction rates of any particular isotope are identical. This does not mean that the isotopic compositions of two compounds at equilibrium are identical, but only that the ratios of the different isotopes in each compound are constant for a particular temperature. During equilibrium reactions, the heavier isotope generally preferentially accumulates in the species or compound with the higher oxidation state. For example, during sulfide oxidation, the sulfate becomes enriched in 8 relative to sulfide (i.e., has a more positive value) consequently,... 

The most illuminating consequence of multi-dimensional vibrational dynamics in polyatomic molecules are fluctuations of resonance widths. In particular, narrow resonances can often be found far above the first dissociation threshold. We have seen that in systems with one degree of freedom the sequence of resonance states is rather short. Since the excitation energy is deposited directly into the reaction coordinate, the complex breaks apart very quickly and the resonances become broad even close to the dissociation threshold. In polyatomic molecules, energy can be temporarily stored in additional degrees of freedom. The lifetime is then determined not only by the total energy, but also by the rate with which the excitation can be redistributed and transferred to the dissociation bond (see the discussion of the classical phase space structure in Sect. 8). 

In this chapter we shall first outline the basic concepts of the various mechanisms for energy redistribution, followed by a very brief overview of collisional intermolecular energy transfer in chemical reaction systems. The main part of this chapter deals with true intramolecular energy transfer in polyatomic molecules, which is a topic of particular current importance. Stress is placed on basic ideas and concepts. It is not the aim of this chapter to review in detail the vast literature on this topic we refer to some of the key reviews and books [JT,... 

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