The correlation between molecular motions and heat capacity in normal ice and water

TL;DR

This study reexamines the heat capacities of ice and water, establishing a detailed correlation between molecular motions and heat capacity, highlighting the roles of vibrations, rotations, and translations.

Contribution

It provides a new, comprehensive description of how molecular motions influence heat capacity in ice and water, emphasizing the significance of translational motions in water.

Findings

Molecular vibrations and rotations contribute to ice's heat capacity.

Translational motions dominate water's heat capacity.

A unified framework links molecular motions to heat capacity in H2O.

Abstract

The heat capacities of ice and water at ambient pressure are reexamined to build an intrinsic correlation between H2O molecular motions and the heat capacity. Based on the evolution of H2O molecular motions, a satisfactory description of the heat capacity of ice and water is provided. The heat capacity of ice is related not only to H2O molecular vibrations, but also to the molecular rotations. In water, all H2O molecular vibrations, rotations and translations contribute to the heat capacity. The molecular translational motions are found to be the main contribution to the large heat capacity of water. The results provide a deep insight into the nature of water and ice at ambient pressure.