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

摘要

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