Full observation of ultrafast cascaded radiationless transitions from S2(ππ-) state of pyrazine using vacuum ultraviolet photoelectron imaging

A photoexcited molecule undergoes multiple deactivation and reaction processes simultaneously or sequentially, which have been observed by combinations of various experimental methods. However, a single experimental method that enables complete observation of the photo-induced dynamics would be of great assistance for such studies. Here we report a full observation of cascaded electronic dephasing from S2(ππ∗) in pyrazine (C4N2H4) by time-resolved photoelectron imaging (TRPEI) using 9.3-eV vacuum ultraviolet pulses with a sub-20 fs time duration. While we previously demonstrated a real-time observation of the ultrafast S2(ππ∗) → S1(nπ∗) internal conversion in pyrazine using TRPEI with UV pulses, this study presents a complete observation of the dynamics including radiationless transitions from S1 to S0 (internal conversion) and T1(nπ∗) (intersystem crossing). Also discussed are the role of 1Au(nπ∗) in the internal conversion and the configuration interaction of the S2(ππ∗) electronic wave function