Matrix Isolation and Theoretical Study on the Photolysis of CH₂ClCOCl

UV light photolysis of chloroacetyl chloride (CH₂ClCOCl) has been investigated using infrared spectroscopy in cryogenic Ar, Kr, Xe and O2 matrices. In all matrices, CHCl=C=O, HCl, CH₂Cl₂and CO were produced, with the relative yields depending on the used matrix gas. The relative yield of CH₂Cl₂ formation to CHCl=C=O formation was greatly enhanced in Xe because of the external heavy atom effect, indicative of the formation of CH₂Cl₂ via the C–C or C–Cl bond cleavage in the triplet state. In CH₂ClCOCl/Ar, photoisomerization from anti- to gauche-CH₂ClCOCl was also observed at the early stage of the irradiation. The results show that in Ar, the reactions predominantly proceed through concerted mechanisms.