Chemical and Thermodynamic Properties of Methyl Chloride Dimer Radical Cations in the Gas Phase

Dimer radical cations of methyl chloride have been prepared in a Fourier transform ion cyclotron resonance mass spectrometer using a consecutive exchange reaction of the xenon dimer radical cation with methyl chloride. Both theory and experiment have indicated the existence of two different stable methyl chloride dimer radical cations, that is a two-center three-electron (2c/3e) bonded dimer radical cation, CH3Cl∴ClCH3•+, with C2 symmetry and a methyl chloride chloronium ylidion structure, CH3Cl·H·ClCH2•+, with Cs symmetry. The CH3Cl∴ClCH3•+ species has been observed to react both as an electron acceptor and as a proton donor. The CH3Cl·H·ClCH2•+ structure, however, reacts only as an electron acceptor. Calculations of the CH3Cl∴ClCH3•+ structure at the MP2/6-311G(d,p) level of theory indicate a bond dissociation energy of 105.4 kJ mol-1 relative to its ionized and neutral monomer products, while experiments show a bond dissociation energy of 109 ± 5 kJ mol-1. The bond dissociation energy of the CH3Cl·H·Cl...