Catching Conical Intersections in the Act; Monitoring Transient Electronic Coherences by Attosecond Stimulated X-Ray Raman Signals

TL;DR

This paper proposes a novel attosecond X-ray Raman spectroscopy technique to directly observe conical intersections in molecules by detecting electronic coherences during photochemical processes.

Contribution

It introduces a new method using femtosecond/attosecond X-ray pulses to directly monitor electronic coherences at conical intersections, surpassing previous indirect detection methods.

Findings

X-ray pulses can directly detect passage through conical intersections

The technique measures electronic coherences, not just populations

Potential for real-time observation of photochemical dynamics

Abstract

Conical intersections (CoIn) dominate the pathways and outcomes of virtually all photophysical and photochemical molecular processes. Despite extensive experimental and theoretical effort, CoIns have not been directly observed yet and the experimental evidence is being inferred from fast reaction rates and some vibrational signatures. We show that short X-ray (rather than optical) pulses can directly detect the passage through a CoIn with the adequate temporal and spectral sensitivity. The technique is based on a coherent Raman process that employs a composite femtosecond/attosecond X-ray pulse to detect the electronic coherences (rather than populations) that are generated as the system passes through the CoIn.