Multi-messenger tracking of coherence loss during bond breaking

TL;DR

This study employs a multi-messenger approach to track real-time electronic and nuclear dynamics during bond breaking in Br₂, revealing the hierarchy of electronic rearrangement and nuclear separation, and establishing a framework for ultrafast molecular imaging.

Contribution

It introduces a coincidence-based multi-messenger method to simultaneously measure electronic and nuclear motions during bond rupture, providing new insights into electron-nuclear coupling dynamics.

Findings

Electronic rearrangement ends before nuclei reach bond-breaking distance.

Br₂ acts as a two-centre interferometer encoding coherence loss.

The approach enables real-time imaging of ultrafast electron-nuclear dynamics.

Abstract

Coupled electronic and nuclear motions govern chemical reactions, yet disentangling their interplay during bond rupture remains challenging. Here we follow the light-induced fragmentation of Br$_2$ using a coincidence-based multi-messenger approach. A UV pulse prepares the dissociative state, and strong-field ionization probes the evolving system. Coincident measurement of three-dimensional photoion and photoelectron momenta provides real-time access to both the instantaneous internuclear separation and the accompanying reorganization of the electronic structure, allowing us to determine the timescale of bond breaking. We find that electronic rearrangement concludes well before the nuclei reach the bond-breaking distance, revealing a hierarchy imposed by electron-nuclear coupling. Supported by semiclassical modelling, the results show that the stretched Br$_2$ molecule behaves as a two-centre interferometer in which the loss of coherence between atomic centres encodes the coupled evolution of electrons and nuclei. Our work establishes a general framework for imaging ultrafast electron-nuclear dynamics in molecules.