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

Guo X, Grützmacher H-F. 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. JOURNAL OF PHYSICAL CHEMISTRY A. 2000;104(33):7811-7820.The ion/molecule reactions of hydrogenated carbon cluster ions CnHx+, n = 18, 20, 24; x = 4-12, in the gas phase with CH3SSCH3 (DMDS) were investigated using Fourier transform ion cyclotron resonance (FT-TCR) spectrometry. The 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 coronene (6), C24H12, by consecutive elimination of H-. atoms using the "soft" activation technique of the sustained off-resonance irradiation collision-induced dissociation (SORI-CID) available on FT-ICR. The products, bimolecular rate constants k(bi), reaction channels and their branching ratios, and SORI-CID fragments of the product ions of the ion/molecule reactions with DMDS provide valuable information about the reactivity and structure of the cluster ions CnHx+. First, it is shown for cluster ions C18Hx+ that the rate constants of the reaction with DMDS of the individual species depend clearly on the structure of the parent polycyclic aromatic hydrocarbon (PAH) of the ions, even for clusters of low hydrogen content. Obviously, the cluster ions remember the skeleton of the parent PAH and, therefore, differ in structure from those formed by laser evaporation of graphite reported by Bowers and co-workers. Second, the bimolecular rate constants increase with decreasing 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 cluster ions. Third, two kinds of the reactivity of the cluster ions CnHx+ with DMDS are observed, i.e., a carbonium-like (C+ reactivity) and an strained aryne-bond-like reactivity (aryne reactivity). Both reactivities display characteristic reaction products with DMDS and can be related to the presence of reaction centers in the cluster ions corresponding to an aryl ion carbenium center, a rr-aryl radical center, and a strained triple bond of an (ionized) 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 the hydrogenated carbon cluster ions with benzene