Time-resolved photoelectron imaging of ultrafast S2→S1 internal conversion through conical intersection in pyrazine

A nonadiabatic electronic transition through a conical intersection was studied by pump-probe photoelectron imaging spectroscopy with a 22 fs time resolution in the benchmark polyatomic molecule of pyrazine and deuterated pyrazine. The lifetimes of the S-2 state of pyrazine and deuterated pyrazine were determined to be 22 +/- 3 fs by the global fitting of the time-energy maps of photoelectron kinetic energy (PKE) distributions. The lifetime of S-3 was determined to be 40-43 fs. Two-dimensional maps of photoelectron distributions were obtained for time (t) and PKE, and individual PKE distributions upon ionization from S-2 and S-1 were extracted. Quantum beat with an approximately 50 fs period was observed after the S-2 -> S-1 internal conversion, which was attributed to the totally symmetric vibration nu(6a) in S-1. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3395206]