ABSTRACT
As reactants transform to products in a chemical reaction, reactant bonds are broken and reformed for the products. Different theoretical models are used to describe this process ranging from time-dependent classical or quantum dynamics [1, 2], in which the motions of individual atoms are propagated, to models based on the postulates of statistical mechanics [3]. The validity of the latter models depends on whether statistical mechanical treatments represent the actual nature of the atomic motions during the chemical reaction. Such a statistical mechanical description has been widely used in unimolecular kinetics [4] and appears to be an accurate model for many reactions. It is particularly instructive to discuss statistical models for unimolecular reactions, since the model may be formulated at the elementary microcanonical level and then averaged to obtain the canonical model.
