INCOHERENT INELASTIC NEUTRON-SCATTERING STUDIES OF PROTON CONDUCTING MATERIALS TRIVALENT METAL ACID SULFATE HYDRATES .1. THE VIBRATIONAL-SPECTRUM OF H5O2+

In order to clarify certain aspects concerning the assignment of bands in the vibrational spectrum of the dihydrated proton H5O2+, the incoherent inelastic neutron scattering spectra of three inorganic compounds containing this ion have been recorded. The spectrum of HClO4·2H2O, obtained at 77 K, unambiguously reflects one type of ordered H5O2+ ion, and contains no contribution from the counterion. Those of the layer structured proton conductors HFe(SO4)2·4H2O and HIn(SO4)2·4H2O, recorded at 20 K, are consistent with the presence of H5O2+ as the only mobile protonic species. The spectra have been fully assigned in terms of vibrations, librations and translations of H5O2+. © 1989