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Title: The structure of CO2 hydrate between 0.7 and 1.0 GPa

A deuterated sample of CO2 structure I (sI) clathrate hydrate (CO2 ∙ 8.3 D2O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO2 hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai, et al. (J. Phys. Chem. 133, 124511 (2010)) and O. Bollengier et al. (Geochim. Cosmochim. AC. 119, 322 (2013)), but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO2 molecules filling the water channels. This CO2+water system has also been investigated using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts an MH-III ‘like’ filled ice structure with considerable disorder of the orientations of the CO2molecule. Furthermore, the disorder appears be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al. our neutron diffraction data shows that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, and recrystallization to sI hydrate occurs upon subsequentmore » heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO2 hydrate transforms directly from the sI form to the filled ice structure.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Science Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Science Division; Carnegie Inst. of Washington, Washington, DC (United States). Geophysical Lab.
  3. National Research Council of Canada (NRC), Ottawa, ON (Canada)
  4. Carnegie Inst. of Washington, Washington, DC (United States). Geophysical Lab.
Publication Date:
OSTI Identifier:
1286804
Grant/Contract Number:
AC05-00OR22725; SC0001057
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 141; Journal Issue: 17; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY