An excess proton in a hydrogen-bonded system enhances the strength of hydrogen bonds of the surrounding molecules. The extent of this influence can be a measure of the number of molecules effectively solvating the excess proton. Such extent in methanol is studied by the observation of the π-hydrogen-bonded OH stretch bands of the terminal sites of protonated methanol clusters, H+(methanol)n, in the gas phase. We performed infrared spectroscopy of H+(methanol)n–benzene clusters in the gas phase. The observed size dependence of the π-hydrogen bonded OH frequency demonstrated that ∼7 molecules effectively solvate the excess proton.
