Photoelectron studies on vibronic coupling in pyrazine

Ionization pathways from the S-1 and T-1 states of pyrazine are investigated using one- and two-photon ionization of the excited state by both resonance enhanced multiphoton ionization photoelectron spectroscopy and zero electron kinetic energy pulsed field ionization techniques. For the triplet manifold, we show that two-photon ionization of T-1 is enhanced by a vibronically induced resonance for which we determine the inducing mode and the nature of the intermediate state, as well as the Rydberg state. For the singlet manifold, we identify the mode responsible for the vibronically induced intensity of a 3p Rydberg state that was previously found to greatly perturb the 1+2(') photoelectron spectrum of S-1 by a resonance at the two-photon level.