Experimental and theoretical investigation into the structural and thermodynamic properties of the mixed methyl halide association radical cations

Abstract

An experimental and theoretical study of the ion/molecule association reactions of methyl halide radical cations with mixed methyl halides (X, Y = I, Br, Cl, F) has been carried out. MS/MS unimolecular and collision-induced dissociation experiments were performed on the association products and provide strong evidence for formation of a two-center three-electron (2 c-3 e) bonded structure, [CH 3X∴YCH 3] ·+, for all association products excluding [C 2H 6FCl] ·+. The [C 2H 6FCl] ·+ results suggest the following atomic connectivity for this association product: [CH 2Cl–H–FCH 3] ·+. Two metastable fragmentation pathways were observed for [CH 3I∴BrCH 3] ·+ and [CH 3Br∴ClCH 3] ·+: direct cleavage of the 2 c-3 e bond and elimination of a methyl group. Only direct cleavage was observed in [CH 3I∴ClCH 3] ·+, [CH 3I∴FCH 3] ·+, and [CH 3Br∴FCH 3] ·+. Kinetic energy release distributions were measured and unimolecular kinetic modeling studies were performed on the metastable reaction pathways. Unimolecular kinetic modeling was carried out using phase space calculations and molecular parameters from density functional theory (DFT) calculations. DFT was also used to investigate the potential energy surfaces for each system.