A DFT assessment of the activation barrier for concerted proton transfer in cyclic water clusters (H2O)n where n = 3–8

Abstract

Currently the proton mobility in water clusters is an area that is relatively unexplored and very important for biochemical and catalytic processes occurring in water. We therefore investigate the barrier for proton transfer in a concerted fashion in water clusters where n = 3–8. Our findings at the B3LYP/aug-cc-pVDZ level of theory indicate that protons can transfer in a low barrier process of 15.5 kJ/mol per H-bond. This is still larger than the average thermal energy at 298 K and therefore suggests that proton tunneling is also happening in water. We reveal the dynamic behavior of protons in cyclic water clusters in which concerted proton transfer occurs through an intermediate Zundel cation. We also offer the proton transfer barrier per H-bond in cyclic water clusters as a function of the size of the water cluster. This study helps in the understanding of the dynamic properties of protons in water.