I. Experimental Spectroscopic Temperature Measurements in the Reflected Wave Region of a Shock Tube Using the OH ²Σ → ²π Band System. II. Shock Tube Measurements of the Absorption Oscillator Strength for the ²Σ → ²π Band System of OH

I. Experimental measurements of the population temperature behind the reflected shock in a shock tube are presented. Emission from two wavelength intervals of the OH ^2Ʃ → ^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 with 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 equilibration 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 ^2Ʃ state from which the emission occurred. II. Previous shock tube measurements of the oscillator strength of the OH ^2Ʃ → ^2π band system made in this Laboratory^(1) have been corrected. Light scattering in the absolute intensity calibration has been eliminated and a continuous flushing technique was used for preparation and introduction of the water vapor-argon test gas mixture into the tube. The experimental technique remains essentially the same as in the earlier studies: hot gas samples at 3100-3500° K were produced behind the reflected shock and the linear rate of increase of absolute spectral intensity in the transparent gas region was measured by monitoring emission from axial observations in the shock tube. The absorption electronic f-number for the ^2Ʃ → ^2π band system has been determined from the measurements as (3.9 ± 0.9) x 10^(-3). This value should be compared with Carrington's ^(2) result of 1.4 x 10^(-3) from absorption measurements in flames, and Oldenberg and Rieke's^(3) value of 1.3 x 10^(-3) and Dyne's ^(4) value of 0.7 x 10^(-3) from measurements in absorption cells.