Styrene clusters in a supersonic jet: Reactive and nonreactive systems

Clusters of styrene with several atoms and small molecules were prepared and studied in a supersonic jet by laser-induced fluorescence (LIF) from S-1 and resonance-enhanced multiphoton ionization (REMPI) using S-1 as the resonant intermediate state. The dissociation limit can be determined in many cases (e.g., for argon, CO2, and ammonia) by recording the excess energy at which fluorescence from the cluster disappears and styrene fluorescence appears. Parent ion signals are easily observable from clusters excited to energies exceeding the dissociation threshold in S-1, as determined by LIF. This indicates a relatively long lifetime of the electronically excited cluster on the ionization time scale. The styrene-trimethylamine system, which is reactive in liquid solution, exhibits a very different fluorescence behavior than all others. Two 1:1 styrene-trimethylamine clusters are observed by fluorescence excitation. One of them exhibits locally excited emission upon absorption near the origin, but at higher excitation energies, the emission is exciplex-type. The other shows exciplex emission at all excitation energies, including the 0-0 band. The data indicate at least two nonradiative processes competing with exciplex formation and with its radiative decay. The relation to solution phase photochemistry is discussed.