Quantum theory of kinetic isotope effects in proton transfer reactions

Abstract

Within the framework of multiphonon electron and atom group transfer theory we have calculated the kinetic isotope effect of proton transfer reactions in homogenous solutions using both harmonic and anharmonic potentials for the proton. The calculations can reproduce all the important features of the isotope effect, such as the maximum for the zero free energy change, and the higher activation energy and Arrhenius pre-exponential factor for the heavier isotope. Quantitative agreement with several experimental data relating to the dependence of the isotope effect on the free energy of reaction and the temperature is furthermore obtained for plausible values of the two parameters required, i.e., the solvent reorganization energy and the proton transfer distance.