Shock-Wave Integrated Intensity Measurements of the 2.7-Micron CO2 Band between 1200° and 3000°K

A shock-wave technique is described which provides a means of measuring the infrared integrated intensity of molecular bands at elevated temperatures. The total band emission from the high-temperature gas region existing between the end plate of a shock tube and the reflected shock wave was measured using a rapid-response infrared detector. The total emission of the band is obtained as a function of pathlength as the reflected shock wave recedes from the end plate. The initial concentration, shock velocity, and reflected-shock pressure were measured and the final conditions of the test gas were calculated from the normal shock relations. The method has been used to measure the absolute intensity of the 2.7 μ band of CO2 (ν1+ν3 and 2ν2+ν3) in the temperature region 1200° to 3000°K. The shock-heated samples were produced in a 4% CO2—96% Ar mixture using helium as a driver gas. To ensure adequate pressure broadening at high temperatures for this weak band and yet to remain within the optically thin region, the measurements were made at approximately 2.5-atm total pressure, 0.1-atm CO2 partial pressure, and CO2 optical path lengths up to a maximum of 0.8 cm·atm. The observed integrated band intensity of the 2.7-μ CO2 band increases by a factor of approximately 2.5 in going from 300° to 3000°K. This variation with temperature is discussed in terms of a simple harmonic-oscillator model.