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 approximately 0.9 eV. The orange color at approximately 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)).