Time-resolved photoelectron imaging of ultrafast S_2 → S_1 internal conversion through conical intersection in pyrazine

摘要

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 μ6a in S_1.