Absorption of Sound in Argon, Nitrogen, and Oxygen at Low Pressures

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Abstract
The amplitude absorption coefficient α for pulsed sound waves in argon, nitrogen, and oxygen has been measured over a range of pressure p from 1 to 10 mm Hg for frequencies f between 60 and 70 kc, the temperature in all cases being held nearly constant at 20°C. For the three gases used, the following experimental values of (pα/f2)107 (cgs units) were obtained: (1) for argon 1.86 with an rms deviation of 0.03, (2) for nitrogen 1.64 with an rms deviation of 0.04, and (3) for oxygen, 1.92 with an rms deviation of 0.03. The corresponding values computed from the classical absorption equation are (1) for argon, 1.87, (2) for nitrogen, 1.31, and (3) for oxygen, 1.61. Thus the absorption in argon is classical while for nitrogen and oxygen the absorption exceeds the classical value. These excesses are attributed to rotational relaxation and the associated relaxation times are calculated in accordance with the thermal relaxation theory of Herzfeld and Rice, and Kneser. For nitrogen, the relaxation time (reduced to STP conditions) is 4.85×10−10 second and for oxygen is 4.95×10−10 second. Both these values are significantly smaller than the values obtained by other workers at higher frequencies.

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