Attosecond Coherent Electron Motion in a Photoionized Aromatic Molecule

TL;DR

This study uses attosecond x-ray pulses to observe and analyze electron motion in a photoionized aromatic molecule, revealing ultrafast charge dynamics relevant to chemical reactions.

Contribution

It demonstrates atomic-site specific tracking of electron motion in molecules using attosecond x-ray pulses combined with computational modeling.

Findings

Sub-femtosecond dynamics linked to non-radiative decay

Few-femtosecond oscillations show electronic wavepacket motion

Provides a benchmark for ultrafast charge motion models

Abstract

In molecular systems, the ultrafast motion of electrons initiates the process of chemical change. Tracking this electronic motion across molecules requires coupling attosecond time resolution to atomic-scale spatial sensitivity. In this work, we employ a pair of attosecond x-ray pulses from an x-ray free-electron laser to follow electron motion resulting from the sudden removal of an electron from a prototypical aromatic system, para-aminophenol. X-ray absorption enables tracking this motion with atomic-site specificity. Our measurements are compared with state-of-the-art computational modeling, reproducing the observed response across multiple timescales. Sub-femtosecond dynamics are assigned to states undergoing non-radiative decay, while few-femtosecond oscillatory motion is associated with electronic wavepacket motion in stable cation states, that will eventually couple to nuclear motion. Our work provides insight on the ultrafast charge motion preceding and initiating chemical transformations in moderately complex systems, and provides a powerful benchmark for computational models of ultrafast charge motion in matter.