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| - Unusual Temperature Dependence of Proton Transfer 3. Classical Kramers' Theory versusthe Landau−Zener Curve-Crossing Formulation
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| - Previously, we measured the proton-transfer rate constant from strong photoacids to several solvents such asalcohols and water as a function of temperature. We found an unusual temperature dependence: at hightemperature the rate constant is almost temperature independent whereas at low temperature the rate constantexhibits a strong temperature dependence and follows the inverse of the dielectric relaxation time of theparticular solvent. We used the Landau−Zener curve-crossing formulation to calculate the proton-transferrate constant. We explained the temperature dependence as a continuous transition from nonadiabatic (high-temperature) to solvent-controlled (low-temperature) limits. In this study, we used the classical Kramers'theory in the medium and strong-damping limits to calculate the transmission coefficient and rate constant.We found good correspondence between the experimental and calculated proton-transfer rate constant at alltemperatures using both models. In both models, the dynamical parameter used to calculate the temperaturedependence of the proton-transfer rate constant is the dielectric relaxation time of the particular solvent.
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