The absorption and dispersion of sound waves in polyatomic gases

It is now generally agreed that the absorption of sound waves in a gas is, in most part, due to the exchange of energy between the sound wave and the translational and internal states of the gas molecules. We develop a theory using the 17-moment approximation1 , from which we are able to calculate the absorption and dispersion of sound in a general polyatomic gas. This theory proves to be general enough to be valid for many internal degrees of freedom, however in our study we consider only rotational and vibrational states. After much arrangement and manipulation it is possible to obtain a set of linear equations which are of the form of a general eigenvalue-eigenvector equation. Such an equation is convenient to be solved on the computer. We develop computer techniques to solve this eigenvalue-eigenvector equation and, using an IBM 360/75 computer, compute the absorption and dispersion. It is found that a combination theory arrived at by adding the classical translational and internal absorption compares favorably with our theory for translational and rotational absorption. Considering vibrational absorption as well, we conclude that we are reasonably accurate although we do not find comparison theories