Rotational ``Temperatures'' of OH in Diluted Flames

Abstract

The effects of gaseous diluents upon the distribution of rotational energies of the electronically excited OH(²Σ⁺) radical in flames at atmospheric pressure have been studied. Helium, argon, nitrogen, and oxygen have been added to stoichiometric mixtures of fuel and oxygen in amounts up to 90 percent of the total volume. In the reaction zones of the acetylene and methane flame diluted with helium, argon, or nitrogen, a departure from rotational equilibrium is found which increases with increasing dilution. This effect is absent in the hydrogen flame and in flames with excess oxygen. Vibrational and electronic nonequilibria are also indicated. These results are consistent with the hypothesis proposed in connection with low pressure studies (see references 2 and 4) that excited OH is formed in an exothermic reaction imparting high rotational energy to the products. Persistence of this rotational energy throughout the radiative lifetime, 10⁻⁶ sec, or 10⁴ collisions, is indicated.