THE PHOTOLYSIS OF WATER VAPOR AND REACTIONS OF HYDROXYL RADICALS

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Abstract
The photolysis of water vapor at 1849 Å has been investigated as a possible source of hydroxyl radicals for kinetic studies. At temperatures from 23 to 350 °C and pressures from 1.3 to 28 mm, H2 and H2O2 were the only detectable products. Experiments with added oxygen indicated that O2 may have been present as an intermediate at a very low steady-state concentration, although this is not certain. Possible mechanisms are discussed.At temperatures from 200 to 350 °C, carbon monoxide appeared to react quantitatively with the hydroxyl radicals produced in the photolysis of water by the reaction, Rates of this reaction relative to those of the reactions, and were estimated from the decrement in the yield of CO2 when H2 or D2 was added to the H2O–CO system, and the following Arrhenius parameters were obtained: At temperatures below 200 °C, hydroxyl radicals were not completely converted to CO2, as the yield of CO2 increased to a maximum, then decreased again, with increasing pressure of CO. The mechanism of this system is complex, but probably involves secondary reactions of HCO or COOH radicals.

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