Indication of Tunneling State of Hydrogen Atom in Hydrogen-Bonded Material 5-Bromo-9-hydroxyphenalenon Studied by X-ray and Neutron Diffractions(Condensed matter: structure and mechanical and thermal properties)

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The dielectric material with an isolated hydrogen-bond, 5-bromo-9-hydroxyphenalenon, was studied by means of neutron and X-ray diffractions in the temperature range between 300 and 10K. Analyses on nuclear and electron density distributions revealed a discrepancy between the two distributions of the hydrogen atom in the hydrogen-bond region, leading to a local electronic dipole moment. Both a least-square structure analysis and the density distribution analysis by the maximum entropy method confirmed that the hydrogen atom occupies two equivalent sites near the center of the hydrogen-bond through the whole temperature range, even at the lowest temperature measured, 10K. This feature, together with previous results on calorimetric, incoherent neutron scattering and far-infrared spectrum measurements, concludes that the hydrogen atom in the hydrogen-bond is in a tunneling state over the two sites. Consequently, 5-bromo-9-hydroxyphenalenon was experimentally identified as a quantum paraelectric material.
社団法人日本物理学会の論文
2008-06-15