HR: 1340h
AN: MR23C-0076    [Abstracts]
TI: Structure and Transport Properties of Hydrogen Filled Ices (H₂O:1/6H₂ and H₂O:H₂) at Pressures to 4 GPa by Solid State Diamond-Anvil-Cell NMR
AU: * Okuchi, T
EM: okuchi@eps.nagoya-u.ac.jp
AF: Department of Earth and Planetary Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8601 Japan
AU: Takigawa, M
EM: masashi@issp.u-tokyo.ac.jp
AF: Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8581 Japan
AU: Shu, J
EM: j.shu@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., NW, Washington, DC 20015 United States
AU: Mao, H
EM: h.mao@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., NW, Washington, DC 20015 United States
AU: Hemley, R J
EM: r.hemley@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., NW, Washington, DC 20015 United States
AU: Yagi, T
EM: yagi@issp.u-tokyo.ac.jp
AF: Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8581 Japan
AB: Hydrogen filled ices are composed of H₂O-ice lattice and hydrogen molecules intercalated to interstitial cavities of the lattice. They can accommodate large amount of hydrogen while keeping the host structure of ices (Vos et al., 1993). At room temperature, their stability field begins at 0.7 GPa and expands to at least 30 GPa. Their properties are important to understand evolution of icy satellites as well as of icy giant planets. However, as for guest hydrogen molecules, not only their local site structures, but also their transport properties, have not yet been reported. We therefore conducted in-situ solid-state NMR of these ices using our state-of-the-art, diamond-anvil-cell high-resolution NMR technique (Okuchi et al, 2005, JCP 122, 244509). Experiments were made at ISSP with 300 MHz custom-made spectrometer. We have developed a novel method to load H₂O-H₂ fluid mixture into sample chambers with almost desired ratio, which is essential to measure the target phase with the maximum S/N. Two known hydrogen filled ice phases and their mixtures have been synthesized at room temperature by finely tuning the applied pressure: The C₁ with ice II host structure and H₂O:H₂ = 6:1, and the C₂ with ice I_c host structure and H₂O:H₂ = 1:1. The H₂O proton resonance in both C₁ and C₂ phases gave broad single-pulse spectrum due to strong dipolar coupling, as fully expected. On the other hand, three molecular hydrogen species in different phases, including fluid H₂, gave rather sharp peaks with well-defined different chemical shifts. These peaks in single-pulse or Hahn-echo measurements indicate fast molecular exchange among the cavity sites, much faster than Larmor frequency. The guest dynamics is therefore quite contrastive to the host lattice. Some interesting mechanical and thermodynamic properties could be predicted from this unique dynamics of hydrogen filled ices.
DE: 0714 Clathrate
DE: 3924 High-pressure behavior
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 5724 Interiors (8147)
DE: 6020 Ices
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005