  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.
