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High-Resolution Adiabatic Calorimetry of Supercooled Water

Liquid water exhibits anomalous behavior in the supercooled region. A popular hypothesis to explain supercooled water's anomalies is the existence of a metastable liquid-liquid transition terminating at a critical point. The hypothesized phase transition is not directly accessible in a bulk experiment because it is expected to occur in "no-man's" region below the kinetic stability limit of the liquid phase at about 235 K, the temperature of homogeneous ice formation. Therefore, verifications of this hypothesis are usually based on extrapolations from the experimentally accessible region. In this work, we present the results of high-resolution adiabatic calorimetry measurements of cold and supercooled liquid water in the range from 294 to 244 K, the lowest temperature of water's supercooling achieved so far in a bulk adiabatic-calorimetry experiment. The resolution of the measurements is also record-high, with the average statistical (random) error of about 0.1 %. The data are consistent with adiabatic-calorimetry measurements of supercooled water earlier reported by Tombari et al. [Chem. Phys Lett., Vol. 300, P. 749 (1999)] but significantly deviate from differential-scanning calorimetry measurements in emulsified water reported by Angell et al. [J. Phys. Chem., Vol. 86, P. 998 (1982)] and by Archer and Carter [J. Phys. Chem B., Vol. 104, P. 8563 (2000)]. Consequences of the new heat-capacity data in interpretation of the nature of water's anomalies are discussed.