Reactivity of CnHx+ (n=24, 18; x=0-12) cluster ions toward benzene

C-24(.+) carbon cluster ions as well as C24Hx+ and C18Hx+ cluster ions of l ow hydrogen content were produced in a FT-ICR spectrometer by repeated loss es of H-. atoms from the molecular ions of coronene C24H12 and of the 4 iso meric 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 observe d due to a fraction of cluster ions with low or no reactivity toward benzen e. The bimolecular rate constants k(bi) of the reactions of all reactive cl uster ions were determined. For C24Hx+ ions the C24H12.+ molecular ions of coronene and the C24H10.+ ions do not undergo a reaction with benzene, whil e for the other C24Hx+ ions the rate constants increase with decreasing num ber x of H-. atoms but exhibit an odd/even alternation. The even-electron C 24H2m+1+ cations are generally more reactive than the C24H2m.+ odd-electron radical cations. The rate constant of the reaction of benzene with the C-2 4(.+) carbon cluster ion eventually produced by SORI-CID from coronene exce eds the rate constant of the same reaction of monocyclic C-24(.+) carbon cl uster ion generated by laser evaporation of graphite by more than 3 orders of magnitude. This shows unambiguously that C-24(.+) cluster ions of a diff erent structure are generated by the SORI-CID technique. It is suggested th at these C-24(.+) ions retain the graphitic structure of the precursor coro nene. This is corroborated by the study of 4 series of C18Hx+ ions derived from the 3 isomeric PAHs. These ions exhibit analogous and as characteristi c reactions with benzene as the C24Hx+ ions, but the rate constants of indi vidual C18Hx+ ions are different for the 4 isomeric precursor PAHs. This in dicates very strongly that all these CnHx+ ions produced by repeated losses of H-. atoms from ionized PAHs with a sequence of SORI-CID procedures reta in the graphitic structures of the precursor molecules.