Matrix Infrared Spectra and Density Functional Calculations for New <i>iso</i>-Halomethanes: CHCl₂–Cl, CHFCl–Cl, CFCl₂–Cl, CHBr₂–Br, and CBr₃–Br in Solid Argon

Laser ablation of transition metals for reactions with halocarbons to produce new metal bearing molecules also exposed these samples to laser plume radiation and its resulting photochemistry. Investigations with CCl₄ also produced several known neutral and charged intermediate species, including the <i>iso-</i>tetrachloromethane CCl₃–Cl observed in previous work and identified by the Maier group. CHCl₂–Cl, CHFCl–Cl, and CFCl₂–Cl, photoisomers of CHCl₃, CHFCl₂, and CFCl₃, were also identified in matrix IR spectra. The new C–X bonds are shorter than those of the reactants, and the Cl atom that is weakly bonded to the residual Cl atom forms an unusually strong C–Cl bond. NBO analysis reveals substantial CCl double-bond character, and the weak Cl···Cl bond is largely ionic. Therefore, the CHX₂–X species can be represented as HXCX^δ+···X^δ−. Ionic properties are revealed for CCl₃–Cl, which has an average C–Cl bond length near the median for the CCl₃ radical and cation and a natural charge of +0.49 for the CCl₃ subunit. IRC computations reproduce smooth interconversion between the reactants and products, and the transition state is energetically close to the product, which is consistent with its disappearance on visible irradiation