An Experimental and Theoretical Investigation of Ion−Molecule Reactions Involving Methyl Halide Radical Cations with Methyl Halides

An experimental and computational study of ion−molecule association reactions of the methyl halides has been carried out. A two-center three-electron bonded species, [CH3X∴XCH3]•+, has been observed for I and Br. MS/MS metastable and collision-induced dissociation experiments provide strong support of the atomic connectivity for both species. Computationally, two [C2H6Cl2]•+ structures have been found: the 2c-3e bonded dimer, [CH3Cl∴ClCH3]•+, and the ylide bound structure, [CH3Cl−H−ClCH2]•+. Both are supported by the MS/MS results which give evidence of the CH2Cl+, CH3Cl•+, and CH3ClH+ fragment ions. The study of [C2H6F2]•+ proved to be somewhat more complicated. Three [C2H6F2]•+ structures were found computationally: the 2c-3e bonded dimer, [CH3F∴FCH3]•+, a dihydrogen bonded structure, [FH2CH−HCH2F]•+, and a hydrogen bonded structure, [CH3F−HCH2F]•+. The F−H bonded species was computed to be the most stable. Kinetic energy release distributions, KERDs, have been measured for all the metastable reaction products and compared with KERD models obtained by using statistical phase space theory. We report here the experimental and theoretical results and the theoretical potential energy surface for all four systems.