Thermal Relaxation in Carbon Dioxide as a Function of Temperature

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Abstract
Sound absorption and velocity measurements have been made in carbon dioxide between 0 and 200°C. The relaxation absorption was isolated by subtracting the tube and classical absorptions from the measured absorption. The Kirchhoff equations, which had been justified previously by measurements in A and N2 were used to make these corrections. From the relaxation absorption were determined the temperature variation of the thermal relaxation time, the transition probability, and the collision efficiency. The results indicate that for the frequencies and pressures here employed the relaxation absorption and velocity effects are a function of f/p. This means that only binary collisions are effective in transferring energy between the vibrational and translational modes. The relaxation theory with a single relaxation time for all the vibrational modes adequately predicts the observed absorption and velocity. It is estimated that a separation in the relaxation times of the two lowest modes by a factor of more than two could not have gone undetected at 100°C. The temperature variation of the collision efficiency was adequately predicted by the Landau-Teller equation.

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