Direct determination of the temperature dependence of proton transfer in the benzoic acid dimer by single crystal neutron diffraction

A single crystal pulsed neutron diffraction study of benzoic acid has been carried out at four temperatures, 20, 50, 100 and 175 K. This has allowed accurate site occupancies to be obtained for the hydrogen atom disorder in the hydrogen bonded carboxylic acid dimer motif. The temperature dependence of the disorder allows the energy difference between the two possible dimer configurations to be obtained. Furthermore it provides unambiguous identification of the lower energy configuration.