Molecular isomer effects in ionization and fragmentation of PAH monomers and clusters: pyrene and fluoranthene

We have investigated collisions between Xe20+ ions and the isolated polycyclic aromatic hydrocarbon (PAH) C16H10 isomers pyrene and fluoranthene or pure clusters of either pyrene or fluoranthene. We show fragment distributions and intensities for both cases and rationalize the results by means of a classical over-the-barrier (COB) model in conjunction with quantum chemistry calculations of vertical ionization energies of pyrene and fluoranthene monomers. We find that comparatively small differences in the first and second ionization energies for these isomers have significant effects on both the monomer and cluster fragment distributions.