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The reaction products of photolysis of acetic anhydride in gas phase at 25"C, where He or C 0 2 was present as buffer gas, were analyzed by gas chromatography. The extent of photodissociation was 52% 2 5% and the extent of intramolecular hydrogen transfer reaction producing acetic acid and ketene was 48% f 5%. The rate constants of the hydrogen exchange and radical combination reactions between methyl and acetyl radicals were calculated from the amounts of products. The value of the ratio of the rate constants of hydrogen exchange and radical combination reactions between methyl and acetyl radicals, k7/k6 = 0.15, indicates that acetyl radical is a relatively poor hydrogen donor. The corresponding ratio of rate constants for the reactions between two acetyl radicals, k , / k , = 0.42, indicates that acetyl radical is a better hydrogen acceptor than methyl radical.

Flash photolysis of dimethyl oxalate produced the radicals CH3, CH30, and COOCH3. Thermally equilibrated methoxycarbonyl radicals did not decompose during radicalradical reactions in the presence of 40-tom cyclohexane in the temperature range 298-448 K. Cyclohexyl radicals were also generated during the flash photolysis of the reaction mixture. Rate coefficients of radical-radical reactions were calculated from the amounts of stable products determined by gas chromatography: CO, COz, CHI, CH3C6H11, and CH30C6Hll. Calculations were performed using an iterative computer integration program. Absolute values of rate coefficients were based on the rate coefficient of the reaction between methyl radicals, k l = 2.7 x 10" dm3 mo1-l sK1, measured with the same equipment.CzH4, CzHfj, CH20, CH,OH, CH3OCH3, HCOOCH,, CH3COOCH3, CH3OCOOCH3,The rate coefficients for reactions (5)-(8) are: k5 = (3.1 + 0.5) X 10" dm3 mol-' s -' k6 = (2.1 + 0.2) X 10" dm3 mol-'s-' k7 = (2.3 + 0.1) x 10" dm3 m o l -'~-~