PUB - Publikationen an der Universität Bielefeld

The stepwise elimination of hydrogen atoms from nine polycyclic aromatic hydrocarbons (PAHs) was investigated by the collision-induced dissociation of the sustained off-resonance irradiation (SORI-CID) technique of Fourier transform ion cyclotron resonance mass spectrometry, In every case the application of sequential SORI-CID resulted in the predominant loss of a single hydrogen atom from the parent ions, and for coronene, perylene, and benz[a]anthracene, this eventually produced pure carbon cluster ions C-n(.+). No carbon cluster ions were observed for small PAHs because of competing fragmentations or insufficient intensities of the parent ions. As a common feature of the larger polycyclic aromatic hydrocarbons studied, hydrogenated carbon cluster ions CnH5+ were produced smoothly after elimination of five hydrogen atoms (from pyrene, C16H10, and fluorene, C13H10) or of seven hydrogen atoms (from coronene, C24H12, perylene, C20H12, benz[a]anthracene, C18H12, chrysene, C18H12, and triphenylene, C18H12), However, uncomplicated further loss of hydrogen atoms to produce cluster ions CnH4+ (or CnH3+) was observed only for benz[a]anthracene, chrysene, and triphenylene. The different dissociations of CnHx+ with odd and even numbers of hydrogen atoms and the difficulty to form CnHx+ (0 less than or equal to x less than or equal to 4) by multisteps of single hydrogen elimination are discussed. The latter observation may be attributed to characteristically different structures of hydrogenated carbon cluster ions CnHx+ with x greater than or equal to 5 and x less than or equal to 4. (Int J Mass Spectrom 185/186/187 (1999) 1-10) (C) 1999 Elsevier Science B.V.