Potential energy barrier for proton transfer in compressed benzoic acid

TL;DR

This study uses simulations to evaluate how high pressure affects the proton transfer barrier in solid benzoic acid, revealing pressure-induced hydrogen bond symmetrization influenced by zero-point energy effects.

Contribution

It provides the first detailed simulation-based analysis of pressure effects on proton transfer barriers in benzoic acid, incorporating zero-point energy considerations.

Findings

Pressure shortens O...O contacts in BA dimers.

Proton transfer barrier decreases with pressure.

Hydrogen bonds become symmetric at high pressure.

Abstract

Benzoic acid (BA) is a model system for studying proton transfer (PT) reactions. The properties of solid BA subject to high pressure (exceeding 1 kbar = 0.1 GPa) are of particular interest due to the possibility of compression-tuning of the PT barrier. Here we present a simulations aimed a evaluating the value of this barrier in solid BA in the 1 atm - 15 GPa pressure range. We find that pressure-induced shortening of the O...O contacts within the BA dimers leads to a decrease in PT barrier, and subsequent symmetrization of the hydrogen bond. However, this effect is obtained only after taking into account zero-point energy (ZPE) differences between BA tautomers and the transition state. The obtained results shed light on previous experiments on compressed benzoic acid, and indicate that a common scaling behavior with respect to O...O distance might be applicable for hydrogen-bond symmetrization in both organic and inorganic systems.