The combination of hydrogen and oxygen photosensitised by nitrogen peroxide

The homogeneous reaction between hydrogen and oxygen has been proved by the work of Hinshelwood, of Haber, and of Semenoff to be a chain reaction, which under certain conditions of temperature and pressure may pass over into an explosive combination. The reaction is subject to the kinetics characteristic of certain types of chain reactions, in that, for any particular temperature, there are upper and lower pressure limits for explosion, the former controlled by deactivation of the chains in the gas phase, and the latter by their termination at the surface. The conditions further point to a branching chain mechanism; below 300°C. there is no observable propagation of reaction chains. These facts seem to be well represented by the scheme of Bonhoeffer and Haber, which was put forward on the basis of a spectroscopic study of the dissociation of steam at high temperatures. H + H2 + O2 = HO + H2 O + 102,000 cals. (1) HO + H2 = H2 O + H + 10,000 cals. (2) reaction (1) sometimes taking the alternative form H + H2 + O2 = OH + OH + H - 2000 cals. (1a) which accounts for the branching of the chains. Reaction (2) does not occur appreciably at temperatures below 300°C., but the OH radicles yield hydrogen peroxide which may be detected.