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

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.