The oxygen-inhibited photochlorination and the chlorine-photosensitized oxidation of tetrachloroethylene and pentachloroethane have been studied in the gas phase at 353-5 and 373.4"K. The rate of chlorination of both compounds is given byand that of oxidation by k and k' for C2HC15 being about 35 % higher than for C2C14. The maximum quantum yield of oxidation is about 300. These results are explained by a mechanism involving the bimolecular radical chain propagating step = 1dO21/(k+k"O21), 2C2c1502 +2C2c150+02. Rate constants have been estimated.

The oxygen effect in the gas-phase photochlorination of trichloroethylene has been investigated at 363 and 403°K in a conventional kinetic apparatus and in a reaction cell combined with a rapid mass spectrometer. Once initiated by light at 4358& the chlorination in presence of oxygen proceeds further in the dark. This " after-effect " has been investigated under various experimental conditions. The results can be represented by a reaction mechanism comprising (i) formation and decomposition of a peroxidic radical, (ii) the accumulation of a semi-stable peroxidic compound during the period of illumination, (iii) its monomolecular decomposition in the gas-phase to give free radicals both in the light and dark periods, (iv) the monomolecular destruction of the semistable peroxide at the wall to yield a stable product(s). Relevant rate constants have been measured. The values obtained and the results of mass spectrometric experiments imply that the semi-stable compound could be a peroxidic dimer such as Cl4HCd--O--C2HCl4.