Studies of the reactions of excited oxygen atoms and molecules produced in the flash photolysis of ozone

The photolytic decomposition of ozone has been further investigated using the technique of flash photolysis. Earlier results have been extended and a detailed mechanism for the production of vibrationally excited oxygen molecules put forward. Comparative studies of the decomposition with and without traces of water present have shown that the $^1$D oxygen atom must be responsible for the chain reaction in both cases. When dry ozone is photolyzed under isothermal conditions, absorption due to vibrationally excited oxygen molecules in their electronic ground states is detected. These molecules are produced by the reaction $O + O_3 \rightarrow O*_2 + O_2$ with up to 17 quanta of vibrational energy, and are rotationally cold. When water is present, however, no absorption due to O$*_2$ occurs but strong OH absorption is seen and it is shown that OH radicals are responsible for propagating the chain reaction in this case. These radicals can only be formed by the reaction $O(^1D) + H_2O \rightarrow 2OH + O_2,$ leading to chain branching. It is an interesting observation that this reaction must be preferred to that with ozone stated above. This conclusion will be examined later. Reactions of $^1$D oxygen atoms with fluorine, chlorine, bromine and hydrogen have also been investigated.