Modeling the effects of thermal fluctuations on proton tunneling kinetics in systems with intermolecular hydrogen bonding

The environmental temperature plays an important role in the kinetics of proton tunneling in biological systems, where molecules are bound through intermolecular hydrogen bonds. Developing a quantum mechanical model that can accurately predict the rate and mechanism of hydrogen transfer is challenging. This study proposes a model in which the donor group is treated using the semiclassical approximation, while the hydrogen bonds, whose geometry is influenced by thermal fluctuations, are modeled as classical springs. This approach allows for a straightforward calculation of how the rates of proton tunneling and the kinetic isotope effects vary with temperature. The model is tested using the formic acid dimer to assess its predictive capability.