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The classical mechanism of chemically activated unimolecular reactions is extended to interpret experimental results in systems olefin/hydrogen atoms. In the case of a large excess of the latter, one has to take into consideration a second chemical activation of the primarily formed radicals by their recombination with H-atoms to yield chemically activated alkane molecules. The radicals as well as the alkane molecules may decompose, and a method based on the coupling of two steady-state master equations is developed to evaluate the contribution of either of the two reaction paths to the ratio decomposition to stabilization. The treatment proposed is demonstrated for the example cis but-a-ene/excess of thermal hydrogen atoms in the presence of molecular hydrogen as a bath gas at 298 K. It turns out that the step via activated butane is not negligible under these conditions.

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The thermal decomposition of biacetyl has been studied at small percentage conversion For these conditions, an almost quantitative The following equation over the temperature range 375-41 7°C. mass balance was obtained by gas-chromatographic analysis. was obtained for the overall reaction loglo k,, = (17.2 + 0.7) -(67400 +z 2300)/4.575TBetween 240" and 277"C, the decomposition of biacetyl initiated by methyl radicals has also been studied. Moreover, the Arrhenius parameters of the following reactions were determined :As source of radicals, the thermolysis of azomethane was used. where A is in sec-' for reaction (1) and in ~m~rno1e-l sec-l for reactions (3) and (4); E is in kcal/mole. Evidence is provided that the displacement reaction (4) proceeds by a twostep mechanism.

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