Experimental Evidence for Anomalous Population Temperatures of OH in Flames

It is the purpose of this note to present an evaluation of the experimental evidence for and against "anomalous" temperatures of OH in flames. Experimental studies have been carried out on low pressure flames, and on flames burning at atmospheric pressure. The results have usually been interpreted by using relations which are applicable only to isothermal systems. Attempts to correct for self-absorption have been made by using isointensity methods. For spectral lines with Doppler contour it has been demonstrated by quantitative calculations that the isointensity methods do not correct for self-absorption unless self-absorption is weak. In particular, Shuler's method, without allowance for the effect of frequency on intensity, has been shown to yield nonlinear plots for strong self-absorption and to be inferior to conventional procedures in the absence of self-absorption. Extensive studies on the effect of self-absorption in falsifying experimental data have been carried out by Cowan and Dieke. We have recently attempted to estimate absolute emission intensities for OH in low pressure flames by using data obtained by Oldenberg and Rieke