kinetic isotope effect

https://doi.org/10.1351/goldbook.K03405
The effect of isotopic substitution on a @O04322@ is referred to as a kinetic @I03327@. For example, in the reaction:
K03405-1.png
the effect of isotopic substitution in reactant A is expressed as the ratio of rate constants $$\frac{k^{\text{l}}}{k^{\text{h}}}$$, where the superscripts $$\text{l}$$ and $$\text{h}$$ represent reactions in which the molecules A contain the light and heavy @I03331@, respectively. Within the framework of @T06470@ in which the reaction is rewritten as:
K03405-2.png
and with neglect of isotopic mass on @T06531@ and the @T06479@, $$\frac{k^{\text{l}}}{k^{\text{h}}}$$ can be regarded as if it were the @E02177@ for an @I03328@ reaction between the @T06468@ [TS] and the @I03338@ reactant A, and calculated from their vibrational frequencies as in the case of a @T06319@. Isotope effects like the above, involving a direct or indirect comparison of the rates of reaction of @I03351@, are called '@I03098@', in contrast to @I03132@, in which a single substrate reacts to produce a non-statistical distribution of @I03352@ product molecules.