Benzene clusters in a supersonic beam - Multiphoton ionization, mass analysis and dissociation kinetics

Abstract

A supersonic beam is employed to produce benzene clusters (C6H6)n up to n=40. Mass analysis is achieved after two-photon ionization in a reflectron mass spectrometer. Photon energy is chosen so that the internal energy of the cluster ions is less than 700 meV and a slow decay on the μs time scale is observed. By an energy analysis with the reflecting field it is found that the elimination of one neutral benzene monomer is the favoured dissociation process of the cluster ions. Information about the dissociation pathways of the cluster ions is essential if one is to obtain neutral cluster abundances from the ion mass spectrum. Furthermore an experimental method is presented to obtain pure intermediate state (S1←S0) spectra of selected clusters without interferences from the other clusters present in the molecular beam. This method is based on the observation of the metastable decay of the corresponding cluster ion. When the metastable signal is recorded as a function of photon energy it reflects the S1←S0 intermediate state spectrum. Spectra are presented for the benzene dimer, trimer, tetramer and pentamer. © 1988 Springer-Verlag.