Supersonic Effects of Water Vapor in CO2 and Their Relation to Molecular Vibrations

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Abstract
Acoustic interferometer measurements at approximately 28°C and atmospheric pressure were made from which the velocity and the absorption in CO2 were computed. Various H2O‐concentrations were used with each frequency, covering the range 284 to 1595 kc/sec. At each frequency, μ (the absorption per wave‐length) rises with increasing humidity to a maximum of about 0.28 and then drops slowly, but with the lower frequencies it also passes through a shelf or minor peak before saturation is reached. As the first absorption peak is approached the velocity drops about 10 m/sec. and a 1‐m/sec. drop occurs near the minor peak. As the frequency is increased the critical H2O‐concentration hm is increased also but at different rates for the two peaks. For the major peak fm = [60+8(10)4h] kc/sec. for the minor peak fm′ = [50+2(10)4h′] kc/sec. Thus the average lifetime of a quantum of vibrational energy is decreased rapidly with humidity. These facts are presented as graphs. They are also correlated with results by other investigators, none of whom has observed a minor absorption peak and dispersion region. Most of these facts are represented quite accurately by theory, the results of which are included.

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