The proton momentum distribution in strongly H-bonded phases of water; a critical test of electrostatic models

TL;DR

This study compares experimental proton momentum distributions in water with theoretical models, revealing that electrostatic models fail to account for quantum vibrational effects below 500 K, indicating the need for more comprehensive approaches.

Contribution

It critically tests electrostatic models against experimental data, showing their limitations in explaining proton behavior in strongly hydrogen-bonded water phases.

Findings

Electrostatic models do not qualitatively match experimental proton distributions below 500 K.

Quantum vibrational zero-point effects significantly influence the enthalpy of vaporization.

Electrostatic effects alone cannot fully explain proton well changes upon solvation.

Abstract

Water is often viewed as a collection of monomers interacting electrostatically with each other. We compare the water proton momentum distributions from recent neutron scattering data with those calculated from two electronic structure based models. We find that below 500 K the electrostatic models are not able to even qualitatively account for the sizable vibrational zero-point contribution to the enthalpy of vaporization. This discrepancy is evidence that the change in the proton well upon solvation cannot be entirely explained by electrostatic effects alone.