Kinetics of OH Radicals from Flame Emission Spectra V. A Study of the Acetylene-Oxygen Flame

Abstract

The inner cone of the acetylene-oxygen flame burning lean (1:5), stoichiometric (2:5), and rich (4:5) at atmospheric pressure has been studied spectroscopically with the object of gaining some information about the elementary processes occurring in this flame. The rotational, vibrational, and electronic distributions of OH(2Σ+) have been determined for each fuel mixture. The analysis of the data showed a rotational Maxwell-Boltzmann distribution with a rotational ``temperature'' several hundred degrees higher than the adiabatic flame temperature. The vibrational distribution of OH(2Σ+) was distinctly nonequilibrium with an excess population in the level v′=3 analogous to that observed for the hydrogen-oxygen flame. This is attributed to the interaction of the 2Σ+ and 2Σ− states of OH. The analysis of the electronic distribution of OH indicated that OH(2Σ+) is present in its thermal equilibrium concentration in the flame at atmospheric pressure. The results of this study in conjunction with the work of Gaydon and Wolfhard on the low pressure acetylene-oxygen flame indicate that the radiation of OH(2Σ+) is to a large extent chemiluminescence so that a considerable fraction of the excited hydroxyl radicals must have been formed in the 2Σ+ state by a chemical reaction (or reactions).