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Structures of high-density and low-density water
1ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom.
Physical Review Letters
|October 6, 2000
Summary
Neutron diffraction reveals water transforms continuously under pressure. Increasing pressure changes water from an open, tetrahedral structure to a high-density form with broken hydrogen bonds.
Area of Science:
- Physical Chemistry
- Materials Science
- Condensed Matter Physics
Background:
- Water exhibits complex structural behavior under varying conditions.
- Understanding water's phase transitions is crucial for many scientific disciplines.
Purpose of the Study:
- To investigate the structural changes in water under pressure at a low temperature.
- To characterize the transformation from low-density to high-density water using neutron diffraction.
Main Methods:
- Neutron diffraction was employed to measure three site-site partial structure factors of water.
- Experiments were conducted at a constant temperature of 268 K and varying pressures.
Main Results:
- A continuous structural transformation was observed with increasing pressure.
- Low-density water (approx. 0.0295 molecules/A^3) with a tetrahedral structure transitions to high-density water (approx. 0.0402 molecules/A^3).
- The high-density form exhibits non-tetrahedral O-O-O angles and a collapsed second coordination shell, indicating broken hydrogen bonds.
Conclusions:
- Increasing pressure induces a continuous structural change in water, not a sharp phase transition.
- Hydrogen bond integrity is compromised in high-density water under pressure.
- The study provides detailed structural insights into water's behavior under pressure.