The concentration of hydroxyl and of oxygen atoms in gases from lean hydrogen-air flames

Abstract

Measurements of OH concentrations in flame gases from lean hydrogen-air flames held on porous burners are reported. [ OH] is always found to be in excess of equilibrium near the flame and to decay downstream. The decay is formally second order in OH and the rate constant is relatively insensitive to pressure, temperature and composition, and has an average value of about 10 −13 cm 3/molecule sec. The effects of the addition of small amounts of nitric oxide have been studied. Data are presented on the relationship between the intensity of light emitted from nitric oxide containing nearly stoichiometric flames and [ OH], and it is argued that these provide strong evidence that the nitric oxide test for O atoms is quantitative. The light-producing reaction is probably NO+ O→ NO 2+hv with a rate constant, k 10, equal to 2 × 10 −18 cm 3 / molecule sec. By means of this test it is shown that under all of the conditions studied oxygen atoms and hydroxyl radicals are equilibrated according to the reaction 2 OH⇌ H 2 O+ O