The Collective Burst Mechanism of Angular Jumps in Liquid Water

TL;DR

This paper uncovers a collective mechanism behind large angular jumps in liquid water, involving cooperative motions of up to 10% of water molecules, using unsupervised learning to analyze hydrogen-bond network fluctuations.

Contribution

It introduces a novel unsupervised learning approach to identify collective reorientational motions and reveals the role of network topology fluctuations in angular jumps.

Findings

Large angular jumps involve highly cooperative motions of up to 10% of water molecules.

Angular jumps are driven by collective fluctuations in hydrogen-bond network topology.

The mechanism involves a cascade of hydrogen-bond fluctuations on the ThZ timescale.

Abstract

Understanding the microscopic origins of collective reorientational motions in aqueous systems requires techniques that allow us to reach beyond our chemical imagination. Herein, we elucidate a mechanism using unsupervised learning, showing that large angular jumps in liquid water involve highly cooperative orchestrated motions. Our automatized detection of angular fluctuations, unravels a heterogeneity in the type of angular jumps occurring concertedly in the system. We show that large orientational motions require a highly collective dynamic process involving correlated motion of up to 10% of water molecules in the hydrogen-bond network that form spatially connected clusters. This phenomenon is rooted in the collective fluctuations of the network topology which results in the creation of defects in waves on the ThZ timescale. The mechanism we propose involves a cascade of hydrogen-bond fluctuations underlying angular jumps and provides new insights into the current localized picture of angular jumps, and in its wide use in the interpretations of numerous spectroscopies as well in reorientational dynamics of water near biological and inorganic systems.