Redistribution reactions energetics

Atoms do not interact spontaneously, unless the electrons on two atoms that come into contact are at different chemical potential energy levels. Such a difference could result from differences in polarizability, which may cause a redistribution of the overall charge density, involving both atoms. In most cases polarization is insufficient cause for chemical reaction, which normally requires activation by external factors. It could be due to energetic collision, thermal activation, high pressure or catalytic effects. The result is the... 

The formation of vibrationally excited products is nearly always energetically possible in an exothermic reaction, and these products can be detected by observing either an electronic banded system in absorption or the vibration-rotation bands in emission. In principle, rotational level distributions may be determined by resolving the fine structure of these spectra, but rotational energy is redistributed at almost every collision, so that any non-Boltzmann distribution is rapidly destroyed and difficult to observe. In contrast, simple, vibrationally excited species are much more stable to gas-phase deactivation and the effects of relaxation are less difficult to eliminate or allow for. 

In view of the great importance of chemical reactions in solution, it is not surprising that basic aspects (structure, energetics, and dynamics) of elementary solvation processes continue to motivate both experimental and theoretical investigations. Thus, there is growing interest in the dynamical participation of the solvent in the events following a sudden redistribution of the charges of a solute molecule. These phenomena control photoionization in both pure liquids and solutions, the solvation of electrons in polar liquids, the time-dependent fluorescence Stokes shift, and the contribution of the solvent polarization fluctuations to the rates of electron transfer in oxidation-reduction reactions in solution. 

The inaccessibility of reaction interfaces to investigation means that indirect methods must be used to explore the chemical reactions that occur within these active zones. The determination of the sequence of bond redistribution steps that results in the transformation of a crystalline reactant into a (usually different but often crystalline) product phase is the fimdamental objective of mechanistic studies [74]. All intermediates and the factors that determine the rate and energetics of the transformation (reactivity) must be identified. 

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