The Interplay of Structure and Dynamics in the Raman Spectrum of Liquid Water over the Full Frequency and Temperature Range

TL;DR

This study combines experimental and simulation approaches to analyze the full Raman spectrum of liquid water across a wide temperature range, revealing how spectral features relate to water's structural order.

Contribution

It introduces a comprehensive analysis of the entire Raman spectrum of water over temperature, linking spectral changes to local tetrahedral order using machine learning potentials.

Findings

The entire Raman spectrum can be modeled as a combination of two temperature-independent spectra.

Certain spectral regions strongly depend on local tetrahedral order.

Changes in structural parameters elucidate the temperature dependence of water's Raman spectrum.

Abstract

While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems.