X-ray absorption signatures of the molecular environment in water and ice

TL;DR

This study uses a many-body approach to calculate x-ray absorption spectra of water and ice, accurately reproducing experimental features and revealing how hydrogen bond dynamics and molecular arrangements influence spectral differences.

Contribution

It introduces a detailed theoretical analysis of x-ray absorption spectra in water and ice, linking spectral features to molecular structure and hydrogen bonding effects.

Findings

Spectra are quantitatively matched with experimental data.

Hydrogen bond breaking enhances pre-edge features in liquids.

Non-bonded molecules influence spectral edges without bond breaking.

Abstract

The x-ray absorption spectra of water and ice are calculated with a many-body approach for electron-hole excitations. The experimental features, including the small effects of temperature change in the liquid, are quantitatively reproduced from molecular configurations generated by ab-initio molecular dynamics. The spectral difference between the solid and the liquid is due to two major short range order effects. One, due to breaking of hydrogen bonds, enhances the pre-edge intensity in the liquid. The other, due to a non-bonded molecular fraction in the first coordination shell, affects the main spectral edge in the conversion of ice to water. This effect may not involve hydrogen bond breaking as shown by experiment in high-density amorphous ice.