Phase Behavior of H2 + H2O at High Pressures and Low Temperatures

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• 作者：Timothy A. Strobel ; Maddury Somayazulu ; Russell J. Hemley
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：March 24, 2011
• 年：2011
• 卷：115
• 期：11
• 页码：4898-4903
• 全文大小：844K
• 年卷期：v.115,no.11(March 24, 2011)
• ISSN：1932-7455

文摘

Whereas several clathrate-like structures are known to exist from mixtures of H₂ + H₂O under pressure, the combined high-pressure and low-temperature region of the phase diagram remains largely unexplored. Here we report a combined Raman spectroscopy and synchrotron X-ray diffraction study on the low-temperature region of the phase diagram. Below 120 K, the H₂ vibron originating from the clathrate 2 (C₂) phase splits into two distinct components, yet X-ray diffraction measurements reveal no structural change between room temperature and 11 K. We suggest that the two vibrons of the C₂ phase at low temperature originate from vibrational transitions of hydrogen molecules in the ground and first excited rotational energy levels. At 1 GPa we observe the clathrate 1 (C₁) phase to persist to the lowest temperature measured (80 K). Upon decompression from the C₂ phase we observed the appearance of cubic ice (I_c), which converted to a new phase before transforming to the C₁ phase. The structure of the new phase is consistent with a water framework similar to 伪-quartz; the structure could also be related to the tetragonal clathrate phase reported previously for nitrogen and argon guests.