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.
Keywords: concerted proton transfer; hetero dimers; hydrogen bonding; pulsed jets; rotational spectroscopy.