The mechanism of the hydrogen-oxygen reaction I. The third explosion limit

One of the outstanding facts about the hydrogen-oxygen reaction is the existence of three distinct Explosion limits, designated, in order of increasing pressure, the first, second and third explosion limits. The influence on the third limit of (a ) hydrogen-oxygen proportions, (b ) additions of nitrogen, carbon dioxide and steam, has been examined: the measurements were made mainly at 586° in a silica vessel coated with potassium chloride (which controls the reaction chains). The results are qualitatively consistent with the theory that the third limit depends upon the (essentially isothermal) branching of reaction chains. An expression based upon the equations OH + H2 = H2 O + H, H + O2 = OH + O, O + H2 = OH + H, H + O2 +M = HO2 +M , HO2 + H2 =H2 O + OH, together with the assumption that HO2 diffuses to the walls of the vessel and is destroyed, leads to a satisfactory description of the third limit as well as of the other two. The constants characteristic of the various gases participating are in fair agreement with those derived by independent means.