Determining the Incorporation of NaCl into Ice VII by Raman Spectroscopy

Details Determining the Incorporation of NaCl into Ice VII by Raman Spectroscopy Determining the Incorporation of NaCl into Ice VII by Raman Spectroscopy

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p51b0444r&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #P51B-0444

Physics

3924 High-Pressure Behavior, 3934 Optical, Infrared, And Raman Spectroscopy, 6218 Jovian Satellites

Scientific paper

High-pressure H2O polymorphs have been thought to comprise the interior of some planetary bodies. Ice VII, a polymorph of H2O with a large range of pressure stability above 2 GPa and room temperature is thought to compose a portion of some Galilean satellites, e.g. Callisto. It has also been hypothesized that these satellites may contain internal salt-water "oceans" (Khurana et al., 1998) that, if present, may affect the distribution of Ice VII at depth. The OH bond in Ice VII has been studied by Raman spectroscopy (Pruzan et al., 1990; Walrafen et al., 1982), however, no data exist on how the bonding structure of Ice VII changes with the incorporation of trace amounts of salt. This study sought to measure the Raman shift in Ice VII formed from NaCl-H2O solutions to 20 GPa. Samples of pure H2O, and 5 wt% NaCl were loaded into a Mao-Bell type Diamond Anvil Cell and Raman spectroscopy was used to analyze the samples at pressure increments of 1-2 GPa. The relative OH stretching frequency was measured to observe the bond structure in Ice VII samples formed from the H2O and NaCl-H2O solutions as pressure increases. OH shifts from the NaCl-H2O solutions were compared to pure H2O measurements observed in this study and also compared to previous studies in the pure H2O system. All results show a negative linear decrease in OH stretching frequency as pressure increases. OH stretching frequency in Ice VII formed from pure water can be represented by the best-fit line: v = 3322.8353 - 23.9857P where P is pressure in GPa and v is the OH stretching frequency in rel cm-1. OH stretching frequencies in Ice VII formed from the 5 wt% NaCl solution was modeled with a linear equation: v = 3338.2502 - 22.6019P. Ice VII formed from 5 wt% data shows a systematic increase of approximately 15 rel cm-1 for any given pressure. From Raman spectra, we hypothesize that NaCl is being incorporated into the bond structure of Ice VII formed from low salinity solutions. Future experiments will be conducted to verify the reproducibility of these experiments, analyze a wider range of salinities and salt compositions, and obtain x-ray diffraction data.

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