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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, th...

Spectral-emissivity measurements of the 4.3-μ CO2 band were made at high temperatures. Under the conditions of the present experiments, the fine structure in the 4.3-μ CO2 spectrum is smeared out and comparable with a weak-line band model. A comparison of the observed spectral emissivities with theoretical band-model calculations shows good agreement. The measured integrated intensity of the 4.3-μ CO2 band between 2650° and 3000°K is 2850 (cm−1/cm at STP) and agrees well with measured room-temperature values.

Spectral emissivities in the 2.7-μ band were obtained for hot gas mixtures of CO2 and H2O between 1000°K and 2200°K for various (CO2/H2O) sample ratios. The emission measurements were made at the exit of a small tripropellant rocket burner which produced the variable (CO2/H2O) mixtures by burning hydrogen, oxygen, and carbon monoxide. The spectral emissivities were determined from a calibrated emission spectrum and a spectroscopic determination of the temperature of the hot gas. The composition was evaluated from a semiempirical fit to a thermochemical flow calculation. The hot CO2–H2O mixtures were observed at a total pressure of 1 atm in the optically thin absorption region with a constant geometric pathlength. The variations of the spectral emissivities as a function of temperature are given for constant density of CO2 and H2O in the optical path. The experimental results agree with semitheoretically derived predictions. The characteristic area ratios of the integrated emissivities or integrated radiances within portions of the 2.7-μ band were derived and given as a function of temperature and (CO2/H2O) sample ratio. These area ratios can be used to determine the (CO2/H2O) concentration in hot gas samples.

A band ratio technique is developed for determining the temperature of optically thin hot gases from the infrared spectrum. The technique is based on the temperature variation of the integrated intensity of combination and overtone bands and not the Planck blackbody function. The technique can be applied to any fundamental, overtone, or combination band pair of a radiating molecule. In particular, the R-branch of the 2.7-μ fundamental band and the 1.87-μ and 1.34-μ combination bands of hot water vapor are investigated as a specific example of the technique. Characteristic band area ratios which can be used to determine the temperature from measured emissivity or radiance spectra are given for H2O. A comparison between temperatures determined from the band ratio technique and temperatures determined by independent experimental methods shows good agreement.