Selected ion flow tube studies of the reactions of H3O+ NO+, and O-2(+) with several aromatic and aliphatic hydrocarbons

We describe the results of a selected ion flow tube study of the reactions of H3O+, NO+, and O-2(+) with the 10 aromatic hydrocarbons benzene, toluene , 1,2-, 1,3-, and 1,4-dimethylbenzene, ethylbenzene, propylbenzene, 1,2,3-, 1,2,3-, and 1,3,5-trimethylbenzene, and 11 aliphatic hydrocarbons which ar e the alkanes A-butane and 2-methyl propane, n-pentane and 2-methyl butane, n-hexane, n-octane, n-decane and n-dodecane, the alkenes 1-pentene and 2-m ethyl-2-butene, and the dialkene 2-methyl butadiene (isoprene). All 30 reac tions of the aromatic hydrocarbons are fast, the rate coefficients k being close to their respective collisional rate coefficients k(c). The H3O+ reac tions all proceed by proton transfer producing the protonated parent molecu les MH+, the NO+ reactions proceed largely via nondissociative charge trans fer producing M+ ions, and the O-2(+) reactions proceed via charge transfer which is partially dissociative in most cases producing M+ and (M-CH3)+ io ns. The k for the 33 aliphatic hydrocarbon reactions are much more varied, ranging from the immeasurable to k(c). Proton transfer is endothermic in th e reactions of H3O+ with the smaller hydrocarbons whilst for the larger hyd rocarbons reactions ion-molecule association occurs producing H3O+.M ions. The NO+ reactions proceed largely via hydride ion transfer producing (M-H)( +) ions, although partial incorporation of the NO+ into thr. larger hydroca rbons with subsequent fragmentation occurs producing minority ions like RHN O+ (where R are radicals like C3H7, C4H9, etc). The O-2(+) reactions all pr oceed by rapid dissociative charge transfer, the number of fragment ions in creasing with the atomicity of the aliphatic hydrocarbon. (Int J Mass Spect rom 181 (1998) 1-10) (C) 1998 Elsevier Science B.V.