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 S-2(pi pi*) 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 S-2(pi pi*) -> S-1(n pi*) internal conversion in pyrazine using TRPEI with UV pulses, this study presents a complete observation of the dynamics including radiationless transitions from S-1 to S-0 (internal conversion) and T-1(n pi*) (intersystem crossing). Also discussed are the role of (1)A(u)(n pi*) in the internal conversion and the configuration interaction of the S-2(pi pi*) electronic wave function. Published by AIP Publishing.