Intermediate range O-O correlations in supercooled water down to 235 K.

Area of Science:

• Condensed matter physics
• Physical chemistry
• Materials science

Background:

• Supercooled water, a metastable liquid phase, exhibits unique properties distinct from normal liquid water.
• Understanding the structure of supercooled water is crucial for various scientific disciplines, including climate science and biology.

Purpose of the Study:

• To investigate the structural evolution of supercooled water using wide-angle X-ray scattering.
• To determine the oxygen-oxygen pair distribution function (PDF) and coordination number at low temperatures.
• To explore the structural differences between supercooled water and amorphous ice.

Main Methods:

• High-energy X-ray scattering experiments were conducted on supercooled water down to 234.8 K.
• The European Synchrotron Radiation Facility (ESRF) was utilized for high-intensity X-ray generation.
• The oxygen-oxygen pair distribution function (PDF) was calculated from scattering data up to an intermolecular distance of approximately 11 Å.

Main Results:

• The 4th and 5th peaks in the PDF of supercooled water increased in height with decreasing temperature.
• The position of the 4th peak (r4) shifted to shorter distances upon supercooling, with a more rapid change observed at the lowest temperatures.
• An isosbestic point was identified in the running oxygen-oxygen coordination number at r_iso = 3.31 ± 0.05 Å, corresponding to a coordination number of 4.39 ± 0.15.

Conclusions:

• The structural changes observed in supercooled water differ significantly from those in amorphous ice.
• The study proposes the existence of 5-member pentamer rings in low-density liquid-like structures within supercooled water.
• These proposed structures correlate with sharp features observed in the PDF at approximately 9 Å and 11 Å.