Reactivity and structure of hydrogenated carbon cluster ions CnHx+ (n = 18, 20, 24; x = 4-12) derived from polycyclic aromatic hydrocarbons by splitting off H center dot atoms: Reactions with dimethyl disulfide

The ion/molecule reactions of hydrogenated carbon cluster ions CnHx+, n = 1 8, 20, 24; x = 4-12, in the gas phase with CH3SSCH3 (DMDS) were investigate d using Fourier transform ion cyclotron resonance (FT-TCR) spectrometry. Th e cluster ions C18Hx+ were prepared from the four C18H12 isomers chrysene ( 1), 1,2-benzanthracene (2), triphenylene (3), and naphthacene (4); cluster ions C20Hx+ from perylene (5), C20H12; and cluster ions C24Hx+ from coronen e (6), C24H12, by consecutive elimination of H-. atoms using the "soft" act ivation technique of the sustained off-resonance irradiation collision-indu ced dissociation (SORI-CID) available on FT-ICR. The products, bimolecular rate constants k(bi), reaction channels and their branching ratios, and SOR I-CID fragments of the product ions of the ion/molecule reactions with DMDS provide valuable information about the reactivity and structure of the clu ster ions CnHx+. First, it is shown for cluster ions C18Hx+ that the rate c onstants of the reaction with DMDS of the individual species depend clearly on the structure of the parent polycyclic aromatic hydrocarbon (PAH) of th e ions, even for clusters of low hydrogen content. Obviously, the cluster i ons remember the skeleton of the parent PAH and, therefore, differ in struc ture from those formed by laser evaporation of graphite reported by Bowers and co-workers. Second, the bimolecular rate constants increase with decrea sing number of hydrogen atoms present and alternate regularly in all series of cluster ions CnHx+ with odd and even number x of hydrogen atoms. These effects parallel the results obtained earlier for the ion/molecule reaction of CnHx+ with benzene and confirm a general reactivity scheme of these clu ster ions. Third, two kinds of the reactivity of the cluster ions CnHx+ wit h DMDS are observed, i.e., a carbonium-like (C+ reactivity) and an strained aryne-bond-like reactivity (aryne reactivity). Both reactivities display c haracteristic reaction products with DMDS and can be related to the presenc e of reaction centers in the cluster ions corresponding to an aryl ion carb enium center, a rr-aryl radical center, and a strained triple bond of an (i onized) aryne. These reactions centers are expected to arise from losses of H atoms from the parent PAH if the polycyclic carbon skeleton survives the fragmentation, as previously suggested from the results of a reaction of t he hydrogenated carbon cluster ions with benzene.