The oxidation of nitrogen monoxide has been studied extensively between 226 and 758 K a t pressures of NO and O2 ranging from about 0.2 to 30 torr. It has been shown that (i) the reaction is properly first order against oxygen and second order against nitrogen monoxide, as well under initial conditions as during the course of the reaction;(ii) the termolecular rate constant, k, first decreases with increasing temperature and reaches a minimum value a t 600 K; (iii) the transition state theory is unable to de-

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.

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The inhibitory eflfect of oxygen on the photochlorination of ethane has been studied between 253 and 423°K. It can be explained by the removal of ethyl radicab by molecular oxygea : C2H5 + 02^C2H502 k9. The value kg = 063 x 10' molei sec~i is in good agreement with literature data. The dependence of the rate on concentrations and light intensity is discussed and permits one to discard an alter native «iplanation involving the reaction CI+O2->C102. * We wish to thank the référée for valuable suggestions. 1 Huybrechts, Martens, Meyers, Olbregts and Thomas, to be published. 2 Goldfinger, Huybrechts and Olbregts, to be published. 3 Dingledy and Calvert, /.

Long-chain chlorine-photosensitized oxidation has been observed in the gas phase at about 355'K for 1,1,2,2-and 1,1,1,2-C~H~C14, CZHClS, and CzC14 but not for CzHe, 1,2-CzH4C12, I,l,I-C2H3C13, CzH4, and 1,2-CzHzCIz. This is shown to depend on the exothermicity of the dissociation of the chloroethoxy radicals which must be involved in each reaction system.