Maxima in the thermodynamic response and correlation functions of deeply supercooled water

• Published in: Science (American Association for the Advancement of Science) Vol. 358; no. 6370; pp. 1589 - 1593
• Main Authors: Kim, Kyung Hwan, Späh, Alexander, Pathak, Harshad, Perakis, Fivos, Mariedahl, Daniel, Amann-Winkel, Katrin, Sellberg, Jonas A., Lee, Jae Hyuk, Kim, Sangsoo, Park, Jaehyun, Nam, Ki Hyun, Katayama, Tetsuo, Nilsson, Anders
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 22.12.2017; The American Association for the Advancement of Science
• Subjects: Chemical Physics; Compressibility; Correlation; Critical point; Divergence; Droplets; Emission; Femtosecond pulses; Heavy water; Isotopes; kemisk fysik; Laser cooling; Loci; Momentum transfer; Scattering functions; Temperature dependence; Thermodynamic properties; Thermodynamics; Vacuum; Water; Water analysis; Water drops; Water sampling; X ray lasers; X-ray scattering
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.aap8269

Femtosecond x-ray laser pulses were used to probe micrometer-sized water droplets that were cooled down to 227 kelvin in vacuum. Isothermal compressibility and correlation length were extracted from x-ray scattering at the low–momentum transfer region. The temperature dependence of these thermodynamic response and correlation functions shows maxima at 229 kelvin for water and 233 kelvin for heavy water. In addition, we observed that the liquids undergo the fastest growth of tetrahedral structures at similar temperatures. These observations point to the existence of a Widom line, defined as the locus of maximum correlation length emanating from a critical point at positive pressures in the deeply supercooled regime. The difference in the maximum value of the isothermal compressibility between the two isotopes shows the importance of nuclear quantum effects.