Origin of OH Chemiluminescence during the Induction Period of the H2–O2 Reaction behind Shock Waves

The intensity and the rate of increase of light emitted by the OH* 2Σ+→2II(0–0) transition were studied during the induction period behind shock waves in 5% H2—95% air mixture. Induction-zone temperatures ranged from about 1000° to 1900°K, and the initial pressure was 10 Torr. A standard lamp was used to calibrate the optical system, so that photomultiplier signals could be transformed to OH* concentration. The results are interpreted in terms of radical-recombination reactions. It is found that OH* is formed in the reaction H+O2+H2→H2O+OH* and is effectively quenched, in these experiments, only by water. The excitation process is an inefficient reaction, with an average rate constant of 2×105 liter2/mole2·sec.