Quantum corrections for rate constants of diabatic and adiabatic reactions in solutions

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Abstract
A method for the calculation of quantized rate constants of chemical reactions in condensed phases is presented. The method focuses on the evaluation of nuclear tunneling corrections for classical activation free energies of diabatic and adiabatic reactions. The diabatic problem is treated by the quasiharmonic dispersed polaron model, using both a second order quantum mechanical rate constant, which is exact for quasiharmonic systems, and a semiclassical approximation based on an analytical density matrix formulation. The adiabatic free energy functionals are obtained by using the corresponding diabatic system as a reference state. A path integral formulation is also used both as a guide for the derivation of the adiabatic correction and as an alternative method for problems of limited dimensionality. The close relationship between the free energy functionals of the present approach and those developed in our earlier studies of electron transfer and proton transferreactions is pointed out. The method is illustrated by studying several simple one and two dimensional problems and by stimulating deuterium isotope effects in proton transferreactions in solutions. The calculations of the isotope effects reproduce the corresponding experimental trend.

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