Experimental spectroscopic temperature measurement in the reflected wave region of a shock tube using the OH^2∑ → ^2Π band system

Abstract

Experimental measurements of the population temperature behind the reflected shock in a shock tube are presented. Emission from two wave length intervals of the OH^2∑ → ^2Π electronic band system was measured photoelectrically, the signals observed being generated by a narrow core of hot gas in the reflected shock region looking axially up the tube. The ratio of the rate of increase of intensity, per unit increase of optical depth, in the two spectral regions is a unique function of the temperature for a transparent gas. The linearity of the signal increase with time represents an experimental verification of the transparency and equilibrium of the test gas. In the temperature range of 3300-4300°K (M_s ~ 4), the measured spectroscopic temperature was in good agreement with the calculated equilibrium temperature, the estimated accuracy of the spectroscopic temperature being ± 75°K. A relaxation time of about 25 µsec was observed for the (2,2) and (3,3) vibration bands to reach statistical equilibrium with the lower (0,0) and (1,1) vibrational levels in the ^2∑ state from which the emission occurred.