Refining the Phase Diagram of Water at Pressure

In a new paper published in The Journal of Physical Chemistry Letters, researchers used infrared absorption spectroscopy to extend the characterization of the boundary between low- and high-density liquid water to the supercooled regime.

Water is central to life, as well as to numerous geological and atmospheric processes. Scientists have long appreciated the fact that water exhibits unusual chemical properties at atmospheric pressure due to hydrogen bonding. Understanding how this behavior changes under the high pressure and temperature conditions of Earth’s interior, however, is challenging.

In a new paper published in The Journal of Physical Chemistry Letters, DCO’s Samuele Fanetti, Roberto Bini, and colleagues at the European Laboratory for Nonlinear Spectroscopy (“LENS”, Firenze, Italy) used infrared absorption spectroscopy to extend the characterization of the boundary between low- and high-density liquid water to the supercooled regime [1]. These data represent the first high-pressure optical measurements at such temperatures. Below 250K, pressure alone dictates the transition between low- and high-density liquid water. Remarkably, this boundary overlaps the transition between ices I and III, and its extension into this “no man’s land” nicely fits the LDA-HDA boundary. These data explain the connection between thermodynamic and metastable regimes, highlighting the existence of two regions, each containing fluid, amorphous, and crystalline phases, strictly related by local structure.  

Understanding these chemical changes at pressure provides insight into the complex behavior of fluids in Earth’s interior, as well as the interiors of other terrestrial planets and moons.

Image: A schemiatic representation of the findings courtesy of Roberto Bini. 

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