Reaction of F atoms with the methyl halides. Vibrational spectra of CH3XF and of H2CX⋅⋅⋅HF trapped in solid argon

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When the products of the reaction between F atoms formed in a microwave discharge and CH3Cl, CH3Br, or CH3I were frozen in a large excess of argon at 14 K, the infrared spectra of the primary reaction products were obtained. Isotopic substitution experiments have provided evidence for two major reaction channels in each of these three reaction systems. Attack of the F atom at the halogen position results in the formation of the CH3XF addition product, which has a moderately strong X–F bond and is photochemically stable at wavelengths as short as 250 nm. F-atom reaction with a hydrogen atom of the methyl halide results in the stabilization of a weakly bound F⋅⋅⋅HCH2X complex, intermediate to the formation of H2CX+HF. For all of the species studied except CH3Cl, the barrier to the decomposition of this complex is sufficiently great to require exposure of the solid deposit to visible light for the production of H2CX and HF. The infrared spectra of the H2CX⋅⋅⋅HF hydrogen-bonded complexes isolated in solid argon are discussed.