Isotope effects in supercooled H$_2$O and D$_2$O and a corresponding-states-like rescaling of the temperature and pressure

Abstract

Water shows anomalous properties that are enhanced upon supercooling. The unusual behavior is observed in both H$_2$O and D$_2$O, 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 (B. Uralcan, et al., J. Chem. Phys. 150, 064503 (2019)), the applicability of this approach for reconciling the differences in temperature- and pressure-dependent thermodynamic properties of H$_2$O and D$_2$O is investigated here. Utilizing previously published data and equations-of-state for H$_2$O and D$_2$O, 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.