Neutron scattering and theoretical studies of Zundel cations in crystalline solids

INOR 1080

Bruce S. Hudson, bshudson@syr.edu, Department of Chemistry, Syracuse University, Syracuse, NY 13244-4100
The Zundel cation, H2O-H-OH2, is an important component of acidic solutions and often occurs in crystalline acid hydrates that have been extensively studied by x-ray diffraction. In perchloric acid dihydrate, HClO4 (H2O)2, this cation is centrosymmetric with four ClO4 groups weakly hydrogen bonded to the four peripheral H atoms. The motion of the central proton in this cation has been the subject of considerable interest including recent gas phase studies. Recent studies of crystalline perchloric acid dihydrate using vibrationally inelastic neutron scattering will be discussed as will be their interpretation on the basis of quantum chemical simulations of the highly anharmonic surface. Much of this work involves the species D2O-H-OD2 which is the dominant species at low temperature, taking advantage of the very much stronger scattering of neutrons by H rather than D. Elastic incoherent scattering experiments that can determine the ground state H atom probability distribution will also be discussed.