Acoustical Studies. III. The Rates of Excitation of Vibrational Energy in Carbon Dioxide, Carbon Disulfide and Sulfur Dioxide

Abstract

Measurements on these three gases at various pressures, temperatures and frequencies are reported. In all cases double collisions provide the predominant mechanism of excitation. The van der Waals or capillary forces follow the acoustical cycle without lag under the conditions of the experiments. The velocity of sound at 9 kc in carbon dioxide shows that a part of the heat capacity has already disappeared from the adiabatic elasticity at this frequency, and comparison with the measurements of other investigators leads to the belief that this term is missing even at considerably lower frequencies at ordinary temperatures. The remaining vibrational energy terms disappear together from the acoustical cycle, their rates of excitation being sensibly equal. There is a considerable activation energy necessary to excite the deformation vibration. The velocity of sound at 9 kc in carbon disulfide agrees well with that obtained by calculation from the results of band spectral analysis and hence no important energy terms appear to be lacking at this frequency. The symmetrical linear (S←C→S) and the deformation (S↓C↑S↓) vibrations leave the acoustical cycle together at high frequencies or at low pressures. A study of the dispersive region caused by this disappearance shows that the rates of excitation of the various energy states are identical within limit of error, and consequently that the activation energy of collision is uniform throughout the dispersive region. The velocity of sound at 9 kc in sulfur dioxide conforms reasonably well to the somewhat conflicting band‐spectral data for the equilibrium heat capacity. There is a serious discrepancy between the results of the velocity measurements in the dispersive region here reported and the current interpretation of the few existing absorption measurements. A tentative argument is given whereby this discrepancy may be removed. Several theoretical questions which require further elucidation are discussed.