Equilibrium and kinetic isotopic fractionation in the CO2 hydration and hydroxylation reactions: Analysis of the role of hydrogen-bonding via quantum mechanical calculations

The formation of H2CO3 and HCO3− from CO2 is common in aqueous environmental systems and occurs via the CO2 hydration and hydroxylation reactions. The reactions are especially important in the context of CaCO3 mineral precipitation. The reactions carry with them equilibrium and kinetic isotope fractionations that impact paleoclimate proxy records. Herein, quantum mechanical calculations of dissolved inorganic carbon species embedded in H2O clusters are analyzed under a transition state theory framework to predict kinetic isotope fractionations associated with the reactions. Experimental measurements of reaction energetics and equilibrium isotope fractionations are well-reproduced by the models which suggests the computational methods are justified.