How water molecules modulate the hydration of CO2 in water solution: Insight from the cluster‐continuum model calculations

The hydration of CO2 in water solution was investigated by the cluster‐continuum model calculations with n = 1–8 water molecules. For n = 1–4 water molecules, all the reactions follow a concerted pathway to the hydration product directly. For n = 5–8 water molecules, all the reactions follow a stepwise mechanism and a labile H3O+ intermediate is involved in reaction. The surrounding water molecules from the bulk solvent play a key role in the proton relay process, which can stabilize the charged transition state and the H3O+ intermediate in reaction. Furthermore, if the proton transfer from H3O+ to the carbonyl oxygen occurs, the hydration pathway will be followed. If there is a proton transfer from H3O+ to the outer water phase through the water bridge, the dissociation product of HCO3− will be formed. The predicted reaction energetics by current cluster‐continuum model calculations shows good agreement with the experimental values. Present calculations strongly suggest the suitable cluster‐continuum model including more explicit water molecules highly required for reasonable and unbiased description of the proton relay mechanism for proton transfer related reactions in water solution. © 2012 Wiley Periodicals, Inc.