Optical Kerr effect of liquid and supercooled water: the experimental and data analysis perspective

TL;DR

This study employs advanced experimental and data analysis techniques in optical Kerr effect spectroscopy to investigate water's molecular dynamics across a broad temperature range, including supercooled states, and compares multiple theoretical models.

Contribution

It introduces innovative experimental and fitting procedures for OKE data analysis, enabling accurate deconvolution and comparison with theoretical models for water dynamics.

Findings

High-quality OKE data for water across temperature range

Schematic mode-coupling model best fits water dynamics data

Data reveals clearer features of supercooled water dynamics

Abstract

The time-resolved optical Kerr effect spectroscopy (OKE) is a powerful experimental tool enabling accurate investigations of the dynamic phenomena in molecular liquids. We introduced innovative experimental and fitting procedures, that permit a safe deconvolution of sample response function from the instrumental function. This is a critical issue in order to measure the dynamics of sample presenting weak signal, e.g. liquid water. We report OKE data on water measuring intermolecular vibrations and the structural relaxation processes in an extended temperature range, inclusive of the supercooled states. The unpreceded data quality makes possible a solid comparison with few theoretical models; the multi-mode Brownian oscillator model, the Kubo's discrete random jump model and the schematic mode-coupling model. All these models produce reasonable good fits of the OKE data of stable liquid water, i.e. over the freezing point. The features of water dynamics in the OKE data becomes unambiguous only at lower temperatures, i.e. for water in the metastable supercooled phase. Hence this data enable a valid comparison between the model fits. We found that the schematic mode-coupling model provides the more rigorous and complete model for water dynamics, even if is intrinsic hydrodynamic approach hide the molecular information.