Equilibria in crystals

Other examples of reversible solid-state reactions in crystals have been described, e.g. conformational changes in organic crystals [25] and spin equilibria in 

2 Transition-State Theory and Free-Energy Relationships 

The rationalization of PER by Marcus is based on a simple model of the reaction profile, that of two intersecting parabolas (Pigure 5.10) [35]. In most applications of the Marcus equilibrium-rate theory, the reaction coordinate is a normalized quantity between 0 and 1, measuring in a generalized way the progress of reaction it is usually poorly defined from a geometrical, structural point of view. Indeed, when the word structure is used in works on PER, it refers mainly to the connectivity 

The lack of structural definition of the reaction coordinate has several unfortunate 

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