An Absorption Technique for Measuring OH Concentrations in Shock Tubes

A spectroscopic technique has been developed and experimentally verified for measuring OH concentrations behind shock waves. A water-cooled, rf-powered lamp was used to generate OH background lines sufficiently narrow to allow the peak absorption technique to be used to compute concentration from the measured absorption. Measurements of absorption by known OH concentrations in incident shock waves over a temperature range from about 1000 K to 2400 K and a pressure range from about 100 Torr to 600 Torr were used to verify the technique. Experimental runs were made with a spectral width containing four lines and another containing eight lines. A quantitative relationship between absorbance and OH concentration was obtained by using a rotationless oscillator strength, f(00) of 8.45 x 10 (-4), and a = 250 (P/T) as the damping constant expression.