Isochores and Heat Capacity of Liquid Water in Terms of the Ion-Molecular Model

Thermodynamics of liquid water in terms of a non-standard approach-the ion-molecular model-is considered. Water is represented as a dense gas of neutral H₂O molecules and single charged H₃O⁺ and OH^- ions. The molecules and ions perform thermal collisional motion and interconvert due to ion exchange. The energy-rich process-vibrations of an ion in a hydration shell of molecular dipoles-well known to spectroscopists with its dielectric response at 180 cm^-1 (5 THz), is suggested to be key for water dynamics. Taking into account this ion-molecular oscillator, we compose an equation of state of liquid water to obtain analytical expressions for the isochores and heat capacity.