High-energy collision-induced dissociation of small polycyclic aromatic hydrocarbons

High-energy collision-induced dissociation (CID) experiments on polycyclic aromatic hydrocarbons (PAHs) having 2-6 rings, naphthalene, anthracene, phe nanthrene, fluoranthene, pyrene and coronene, were performed, and the relat ive abundances of their fragment ions were investigated as a function of co llision energy. The results revealed that the PAHs except naphthalene showe d a bimodal-type distribution of positive fragmentation ions, which is clos ely similar to the fragment-ion distribution reported for the CTD of three- dimensional fullerene, C-60(+) and C-70(+). The three-ring isomers of anthr acene and phenanthrene and the four-ring isomers of fluoranthene and pyrene can be distingushable in their spectra under an electron ionization energy of 70 eV, but the high-energy CID spectra of the three- and four-ring isom ers were almost identical. The fragmentation corresponding to fragment ions in the low-mass region of the bimodal CID spectra could be interpreted by the simple statistical model that fragment ions are formed by random evapor ation from the molecular ions after a considerable structural rearrangement , 'phase transition', occuring at some high-energy state. Copyright (C) 200 0 John Wiley & Sons, Ltd.