Kimmel Greg A
Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
J Chem Phys. 2024 May 21;160(19). doi: 10.1063/5.0207719.
Water shows anomalous properties that are enhanced upon supercooling. The unusual behavior is observed in both H2O and D2O, however, with different temperature dependences for the two isotopes. It is often noted that comparing the properties of the isotopes at two different temperatures (i.e., a temperature shift) approximately accounts for many of the observations-with a temperature shift of 7.2 K in the temperature of maximum density being the most well-known example. However, the physical justification for such a shift is unclear. Motivated by recent work demonstrating a "corresponding-states-like" rescaling for water properties in three classical water models that all exhibit a liquid-liquid transition and critical point [Uralcan et al., J. Chem. Phys. 150, 064503 (2019)], the applicability of this approach for reconciling the differences in the temperature- and pressure-dependent thermodynamic properties of H2O and D2O is investigated here. Utilizing previously published data and equations-of-state for H2O and D2O, we show that the available data and models for these isotopes are consistent with such a low temperature correspondence. These observations provide support for the hypothesis that a liquid-liquid critical point, which is predicted to occur at low temperatures and high pressures, is the origin of many of water's anomalies.
水表现出异常性质，过冷时这些性质会增强。在H₂O和D₂O中均观察到这种异常行为，不过，这两种同位素的温度依赖性不同。人们常指出，比较两种同位素在两个不同温度下的性质（即温度偏移）大致可以解释许多观测结果——最大密度温度偏移7.2 K是最著名的例子。然而，这种偏移的物理依据尚不清楚。受近期工作的启发，在三个均呈现液-液转变和临界点的经典水模型中，水的性质表现出“类对应态”重标度[乌拉尔坎等人，《化学物理杂志》150, 064503 (2019)]，本文研究了这种方法在调和H₂O和D₂O的温度和压力依赖热力学性质差异方面的适用性。利用先前发表的H₂O和D₂O的数据及状态方程，我们表明这些同位素的现有数据和模型与这种低温对应关系一致。这些观测结果支持了以下假设：预计在低温高压下出现的液-液临界点是水的许多异常现象的根源。
