Probing Ultrafast Internal Conversion through Conical Intersection via Time-Energy Map of Photoelectron Angular Anisotropy

The ultrafast S-2 -> S-1 internal conversion of pyrazine through a conical intersection of the potential energy surfaces was clearly observed by ultrafast photoelectron imaging. The 2D time-energy map of the photoelectron angular anisotropy revealed a clear signature of the internal conversion (the color change of green-orange-green in the horizontal direction) at similar to 0.9 eV. The orange color at similar to 20 fs and 0.9 eV was found to correspond to the non-Koopmans ionization process from S-2(pi,pi*) to D-0(n(-1)).