Selected ion flow tube studies of the reactions of H 3O +, NO +, and O 2+ with several aromatic and aliphatic hydrocarbons

Abstract

We describe the results of a selected ion flow tube study of the reactions of H 3O +, NO +, and O 2 + with the 10 aromatic hydrocarbons benzene, toluene, 1,2-, 1,3-, and 1,4-dimethylbenzene, ethylbenzene, propylbenzene, 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzene, and 11 aliphatic hydrocarbons which are the alkanes n-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-methyl-2-butene, and the dialkene 2-methyl butadiene (isoprene). All 30 reactions of the aromatic hydrocarbons are fast, the rate coefficients k being close to their respective collisional rate coefficients k c . The H 3O + reactions all proceed by proton transfer producing the protonated parent molecules MH +, the NO + reactions proceed largely via nondissociative charge transfer producing M + ions, and the O 2 + reactions proceed via charge transfer which is partially dissociative in most cases producing M + and (M–CH 3)+ ions. The k for the 33 aliphatic hydrocarbon reactions are much more varied, ranging from the immeasurable to k c . Proton transfer is endothermic in the reactions of H 3O + with the smaller hydrocarbons whilst for the larger hydrocarbons reactions ion–molecule association occurs producing H 3O +.M ions. The NO + reactions proceed largely via hydride ion transfer producing (M–H) + ions, although partial incorporation of the NO + into the larger hydrocarbons with subsequent fragmentation occurs producing minority ions like RHNO + (where R are radicals like C 3H 7, C 4H 9, etc). The O 2 + reactions all proceed by rapid dissociative charge transfer, the number of fragment ions increasing with the atomicity of the aliphatic hydrocarbon.