Matrix Infrared Spectra, Photochemistry and Density Functional Calculations of Cl^––HCCl₂, ClHCl^–, Cl–ClCCl, and Cl^––HCHCl Produced from CHCl₃ and CH₂Cl₂ Exposed to Irradiation from Laser Ablation

Strong absorptions for Cl^––HCCl₂ with D and ¹³C isotopes were observed in the spectra of CHCl₃ codeposited with laser-ablated metal atoms, cations, electrons, and vacuum ultraviolet radiation, which shows that the precursor is an effective electron scavenger. The IR spectra, isotopic shifts, and DFT calculations identified the major product as Cl^––HCCl₂, which is characterized by a strong, broad C–H stretching mode interacting with the overtone of the H–C–Cl bending fundamental. These absorptions decreased on subsequent annealing and photolysis treatments while the ClHCl^– absorptions increased, suggesting that dissociation of the chloroform anion generates the stable symmetrical hydrogen dichloride anion as does the reaction of HCl and Cl^–. A new set of strong, broad absorptions in the deposition spectra that diminished on the early annealing and photolysis are assigned to the Cl–ClCCl radical isomer. Dominant spectral features in the C–H stretching region for the experiments with CH₂Cl₂ are assigned to the symmetric C–H and the antisymmetric Cl–H–C–H stretching bands of the methylene chloride anion Cl^––HCHCl. The stronger, broader, lower frequency bands are due to the hydrogen-bonded hydrogen stretching, and the weaker, sharper, higher frequency absorptions are due to the terminal C–H bond stretching. Similar experiments with CHBr₃ produced absorptions for the analogous Br^––HCBr₂ and BrHBr^– anions.