Proton Tunneling in Heterodimers of Carboxylic Acids: A Rotational Study of the Benzoic Acid-Formic Acid Bimolecule.

Tunneling effects have been measured in the pulsed jet Fourier transform microwave spectra of two isotopologues of the benzoic acid–formic acid bimolecule. The tunneling splittings are originated by the concerted proton transfer of the two carboxylic hydrogens. From the values of these splittings for the OH–OH and OD–OD species, it has been possible to model/size the barrier to the concerted double proton transfer.