Effect of Temperature on the Rotational and Vibrational Relaxation Times of Some Hydrocarbons

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Abstract
Ultrasonic velocity and absorption measurements in methane, ethylene, ethane, and propane are reported. The temperature range is from room temperature to 800°C, and the frequency/pressure range encompasses both the vibrational and the apparent rotational relaxation. In methane and ethylene the vibrational relaxation time of the lowest frequency mode varies with exp (T −1/3 ) , while the apparent rotational relaxation time increases with temperature. Evidence is presented that the vibrational and rotational degrees of freedom are excited independently, even when the time constants are within a factor of 15 of each other.

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