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.
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 absorption coefficients of the ν3, 4.3-μ CO2 band were measured over a temperature range of about 1200° to 2400°K at various pathlengths. The hot CO2 sample was investigated in the exhaust jet of a small supersonic burner, while the jet composition was obtained using a radiation temperature measurement and a simple thermochemical calculation. The present experimental results are compared with existing experimental values and theoretical calculations. The results indicate that above 2000°K a weak line approximation can be used to describe the absorption or emission of the band. The apparent integrated band intensity of the CO2 fundamental as a function of temperature is also reported and discussed in relation to other measurements.
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