The Bethe surface of liquid water

Area of Science:

• Physics
• Physical Chemistry
• Materials Science

Background:

• The Bethe surface is a key descriptor of the dynamic structure of liquid water.
• Previous calculations relied on semiempirical models, necessitating experimental validation.

Purpose of the Study:

• To compare the semiempirical model's Bethe surface for liquid water with recent inelastic X-ray scattering (IXS) data.
• To assess the agreement between theoretical calculations and experimental observations.

Main Methods:

• Utilized recently available inelastic X-ray scattering (IXS) data for liquid water.
• Compared experimental data with previously calculated Bethe surfaces derived from a semiempirical model.
• Applied the Bethe sum rule to constrain and validate both datasets.

Main Results:

• No significant discrepancies were found between the global view of the Bethe surface from the model and IXS experiments.
• The Bethe ridge shape from IXS data is broader than predicted by the impulse approximation.
• Extrapolation to the optical limit was performed and data reliability was assessed.

Conclusions:

• The semiempirical model provides a reliable representation of the Bethe surface for liquid water when compared to IXS data.
• The broader Bethe ridge in experimental data suggests limitations of the impulse approximation for describing liquid water dynamics.
• The study validates theoretical models against advanced experimental techniques, enhancing our understanding of liquid water.