Kinetics of OH Radicals from Flame Emission Spectra. IV. A Study of the Hydrogen-Oxygen Flame

Abstract

The inner and outer cones of hydrogen-oxygen flames burning lean (1:1), stoichiometric (2:1), and rich (4:1, 6:1) at atmospheric pressure have been studied spectroscopically with the object of gaining some information as to the elementary processes occurring in this flame. The rotational, vibrational, and electronic distribution of OH(2Σ+) has been determined for both the inner and outer cone of each fuel mixture. A thermal equilibrium distribution of the internal degrees of freedom was found for OH(2Σ+) in the outer cones for all fuel ratios; in the inner cones there was a vibrational nonequilibrium distribution indicated by an excess population of the levels v′=2 and 3. It is suggested that this nonequilibrium may be due to a radiationless transition reaction involving H or O atoms in excess of their thermal concentrations. This assumes, in agreement with the suggestion of Gaydon and Wolfhard, that the 2Σ+ state of OH is weakly predissociated between the levels v′=2 and 3 by a 2Σ− state. The possible significance of this excess atomic concentration for the active particle diffusion theory of flame propagation is indicated briefly. It is concluded that the radiation of OH(2Σ+) in the oxy-hydrogen flame is predominantly thermal.