Non-unit kinetic isotope effects

Non-unit kinetic isotope effects such as the rate-constant ratio kn/k-Q also derive from isotopic zero-point energy differences in the reactant state and in the transition state. A second manifestation of the Uncertainty Principle may also contribute to kinetic isotope eff ects, namely isotopic differences in the probability of quantum tunneling through the energy barrier between the reactant state and the product state. 

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