Spectroscopic studies of the hydrogen-oxygen explosion initiated by the flash photolysis of nitrogen dioxide

Abstract
The method of flash photolysis has been used to initiate the reaction between hydrogen and oxygen, using a small amount of nitrogen dioxide as sensitizer. The dependence of the ignition limits on total pressure, capacity and the pressure of nitrogen dioxide have been studied, as well as the flash photochemical decomposition of nitrogen dioxide alone. The explosive reaction is complete in a few milliseconds, and very short induction periods are found whose duration can be explained in terms of the initial temperature rise. It is shown that the initiation of the explosion in this way is reproducible to less than 10-4 s and flash spectroscopy is used to study the development of the reactions with time. The spectra obtained are described and the reactions of the OH radical are investigated by means of its absorption spectrum , whose intensity variations with partial pressure of hydrogen, oxygen, nitrogen and water vapour over time intervals of 0·2 ms throughout the reaction are given. Addition of hydrogen accelerates the reaction, but oxygen in excess has the same effect as an inert gas which is to decrease the rate. It is shown that the important propagation steps are exclusively bimolecular and the main reactions of the OH radical are identified. The mechanism of the overall explosion reaction is discussed and a reaction scheme is given which is in accordance with the results.