Time-resolved photoelectron imaging of S2 → S1 internal conversion in benzene and toluene

Ultrafast internal conversion of benzene and toluene from the S-2 states was studied by time-resolved photoelectron imaging with a time resolution of 22 fs. Time-energy maps of the photoelectron intensity and the angular anisotropy were generated from a series of photoelectron images. The photoelectron kinetic energy distribution exhibits a rapid energy shift and intensity revival, which indicates nuclear motion on the S-2 adiabatic surface, while the ultrafast evolution of the angular anisotropy revealed a change in the electronic character of the S-2 adiabatic surface. From their decay profiles of the total photoelectron intensity, the time constants of 48 +/- 4 and 62 +/- 4 fs were determined for the population decay from the S-2 states in benzene and toluene, respectively. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3586809]