The pulsed field ionization spectrum and lifetimes of the states at the S1 origin of pyrazine

The pump–probe pulsed field ionization (PFI) spectrum through the origin of S1 of pyrazine reveals three distinct types of peaks. At low excess energy above the lowest ionization potential (I.P.) are sharp peaks with Franck–Condon factors representative of the singlet intermediate state. At ionization wavelengths <208 nm, the Franck–Condon overlap allows for the observation of primarily the triplet component of the pumped superposition state. At this energy, some resolved structure has a measured lifetime >10 μs and is determined to be the result of ionization of relaxed triplet states populated through vibrational dissociation of van der Waals clusters. A diffuse structure in the same region is the result of ionization of monomer intermediate states with lifetimes that vary with the ionizing wavelength. From this variation, it can be surmised that there is an inhomogeneous sample of intermediate states, possibly due to a mixture of unrelaxed molecular eigenstates and decoupled triplets populated by an intramolecular vibrational relaxation within the triplet manifold.