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Spectral emissivities of the overtone and combination bands of H2O in the 1‐ to 2‐μ region have been measured between 1000° and 2200°K. The hot water vapor samples were produced in a small supersonic burner using H2 and O2. The measurements were made at the exit of the burner where the interactions of the hot gas jet with the ambient atmosphere are small. The variation of the spectral emissivities of H2O in the optically thin absorption region as a function of temperature are given for a total pressure of 1 atm and a constant amount of H2O in the optical path.The integrated intensities of the bands have been determined from the emissivity spectra at the various temperatures. The values of the integrated intensities of the 1.87‐, 1.38‐, and 1.14‐μ H2O bands at 273.2°K are 26.0, 21.2, and 1.92 (cm—2·atm—1), respectively. The integrated intensity variations with temperature of the bands have been used to determine the absolute intensity contributions from the numerous overtone and combination transitions whi...

The temperature dependencies of the total integrated intensities of vibrational—rotational band systems are discussed and general expressions are given for the temperature dependencies for the harmonic oscillator approximation. The derived dependencies indicate that while the total integrated intensity of a fundamental is independent of temperature, the integrated intensity of an overtone or combination band system increases with increasing temperature. The theoretically derived temperature dependencies are compared with available experimental data and good agreement is found where self absorption within the test gas does not influence the experimental results.

The absolute intensities of the two infrared active fundamentals of the ammonium ion, ν3 and ν4, have been studied in several environments. Dilute solid solutions of NH4+ ions in KCl, KI, CsCl, and CsI were studied and compared with pure NH4I. After separating the effect of the net charge, the apparent bond moments ranged from 0.63 d to 0.80 d (av 0.71) and the bond dipole derivatives, ∂μ/∂r, from 2.06 d/A to 3.59 d/A (av 2.80 d/A). The bond moment is substantially the same as in NH3.

Measurements have been made of the total integrated band intensities of the 5.3‐μ fundamental and the 2.7‐μ first overtone bands of NO in the temperature range 1400° to 2400°K. The NO gas sample was studied at high temperatures using a reflected shock‐wave technique.Within the temperature range used in the present experiments, the integrated band intensity of the NO fundamental does not vary. However, the integrated intensity of the first overtone band of NO shows a small temperature dependence. The temperature dependencies of the two bands are in agreement with theoretical temperature dependencies determined assuming a harmonic oscillator approximation to the NO molecule. Using the theoretical temperature dependencies the experimental data have been extrapolated to give values of the integrated intensities α° at STP. The values of α° obtained for the fundamental and first overtone bands of NO are 76±7 cm—2·atm—1 and 2.8±0.5 cm—2·atm—1, respectively.

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...

The monohydrates of the hydrogen halides exist as ionic crystals. The infrared spectra of OH3F, OH3Cl, OH3Br, OH3I, and OD3Cl at —195°C showed the four fundamental frequencies expected for a symmetrical pyramid at about 1100 cm—1 (ν2), 1700 cm—1 (ν4), 2600 cm—1 (ν1 or ν3), and 3200 cm—1 (ν1 or ν3). The high‐frequency bands, which are very broad at —195°C, did not sharpen on cooling to 8°K, indicating that their breadth is caused by some frozen‐in disorder.

Measurements have been made of the total absolute integrated intensities of the 4.7‐μ fundamental and 2.4‐μ first overtone band systems of CO at various temperatures within the range 2500° to 5000°K. The CO gas sample was studied in emission using a reflected shock wave to raise the sample to the high temperatures. Effects of vibrational relaxation, dissociation, and shock structure have been considered in the data interpretation.Within the temperature range used in the present experiments, the integrated intensity of the CO fundamental band system remains constant. However, the integrated intensity of the CO first overtone band system shows a small increase with increasing temperature. The temperature dependencies of the two band systems are in agreement with the theoretical temperature dependencies. The present experimental results for CO extrapolated to STP are 289±29 and 2.3±0.3 cm−2·atm−1 for the total integrated band intensities of the fundamental and first overtone band systems, respectively.

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.

Spectral-emissivity measurements of the 15-μ band of CO2 were made in the temperature range from 1000° to 2300°K. The hot gas was produced in a supersonic burner, which used gaseous carbon monoxide and oxygen as propellants. Many “hot” transitions were observed which were identified through their Q-branches even when the spectral resolution of the spectrometer was not very high. The total intensity of the ν2-fundamental band system was determined at the highest temperatures and a value of 240 ± 15% cm−1/cm at STP was obtained in the present experiment which is in agreement with other measurements at room temperature. The maximum error resulting from the presence of the strong central Q-branch (at 670 cm−1) at a temperature of 2300°K was estimated, utilizing detailed line calculations for the fundamental transition and band-model calculations for the higher-order transitions.

Spectral emissivities have been obtained for the 2ν2+ν3 and ν3+ν1 carbon dioxide combination bands between 3100 and 3800 cm−1 at 1200°, 1500°, and 1800°K. Heated CO2 was produced in a 150-lb-thrust rocket burner burning gaseous carbon monoxide and oxygen. Emission measurements were made on the expanded exhaust gas of the burner where the composition, total pressure, and temperature could be defined. The spectral emissivities were determined from a calibrated emission spectrum and a spectroscopic determination of the temperature of the test gas. The hot CO2 samples were observed at a total pressure of 1 atm in the optically thin region where the highest spectral emissivities at 3700 cm−1 were about 0.1. The spectral emissivity curves were used to obtain the integrated intensity of the 2.7-μ CO2 band at the high temperatures. The variations of the spectral emissivities and integrated intensities with temperature agree with previous predictions.

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.