PUB - Publikationen an der Universität Bielefeld

C-24(.+) carbon cluster ions as well as C24Hx+ and C18Hx+ cluster ions of low hydrogen content were produced in a FT-ICR spectrometer by repeated losses of H-. atoms from the molecular ions of coronene C24H12 and of the 4 isomeric polycyclic aromatic hydrocarbons (PAH) C18H12 triphenylene, chrysene, 1,2-benzanthracene, and 2,3-benzanthracene, respectively, using a sequence of SORI-CID procedures. Then, the selected cluster ions were reacted with benzene and benzene-d(6) to yield product ions [CnHx. nC(6)H(6)](+), n = 1-3, and [CnHx-1. nC(6)H(6)](+). In the latter case it was proven by reaction with C6D6 that the H-. atom lost originates exclusively from the CnHx part of the original cluster ions. In most cases, bimodal kinetics were observed due to a fraction of cluster ions with low or no reactivity toward benzene. The bimolecular rate constants k(bi) of the reactions of all reactive cluster ions were determined. For C24Hx+ ions the C24H12.+ molecular ions of coronene and the C24H10.+ ions do not undergo a reaction with benzene, while for the other C24Hx+ ions the rate constants increase with decreasing number x of H-. atoms but exhibit an odd/even alternation. The even-electron C24H2m+1+ cations are generally more reactive than the C24H2m.+ odd-electron radical cations. The rate constant of the reaction of benzene with the C-24(.+) carbon cluster ion eventually produced by SORI-CID from coronene exceeds the rate constant of the same reaction of monocyclic C-24(.+) carbon cluster ion generated by laser evaporation of graphite by more than 3 orders of magnitude. This shows unambiguously that C-24(.+) cluster ions of a different structure are generated by the SORI-CID technique. It is suggested that these C-24(.+) ions retain the graphitic structure of the precursor coronene. This is corroborated by the study of 4 series of C18Hx+ ions derived from the 3 isomeric PAHs. These ions exhibit analogous and as characteristic reactions with benzene as the C24Hx+ ions, but the rate constants of individual C18Hx+ ions are different for the 4 isomeric precursor PAHs. This indicates very strongly that all these CnHx+ ions produced by repeated losses of H-. atoms from ionized PAHs with a sequence of SORI-CID procedures retain the graphitic structures of the precursor molecules.