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

An experimental and theoretical study of the ion/molecule association react ions 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 d issociation experiments were performed on the association products and prov ide strong evidence for formation of a two-center three-electron (2c-3e) bo nded structure, [CH3X therefore YCH3](.+), for all association products exc luding [C2H6FCl](.+). The [C2H6FCl](.+) results suggest the following atomi c connectivity for this association product: [CH2Cl-H-FCH3](.+). Two metast able fragmentation pathways were observed for [CH3I therefore BrCH3](.+) an d [CH3Br therefore ClCH3](.+): direct cleavage of the 2c-3e bond and elimin ation of a methyl group. Only direct cleavage was observed in [CH3I therefo re ClCH3](.+), [CH3I therefore FCH3](.+), and [CH3Br therefore FCH3](.+). K inetic energy release distributions were measured and unimolecular kinetic modeling studies were performed on the metastable reaction pathways. Unimol ecular 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 . (C) 1999 Elsevier Science B.V.