Time-resolved photoelectron spectroscopy from first principles: Excited state dynamics of benzene

We use the ab initio multiple spawning (AIMS) method to follow the dynamics of benzene after excitation to the second singlet excited state (S-2). The results are validated by comparison to potential energy surfaces including dynamical electron correlation effects. Time-resolved photoelectron spectra are computed and compared to experimental results. Simulations agree with experiment that there are both short-lived and long-lived components of the excited state population. We show that these components both originate from quenching through the same S-2/S-1 conical intersection and that the difference between them comes from their behavior immediately after decay to S-1. This is presumed to be a function of the details of the way in which the S-2/S-1 intersection region is accessed; for example, the momentum distribution and the topology of the seam in the relevant region.