Vibrational and Rotational Relaxation in Ammonia

Abstract

Ultrasonic absorption has been measured in ammonia in the temperature range 300–773°K over the f/p range 1–100 MHz/atm. This data was analyzed to obtain vibrational and rotational relaxation times and collision numbers. The vibrational collisions numbers are unusually small and decrease only slightly with increasing temperature. The maximum in the collision number predicted by Shin's theory for polar molecules is not observed. The temperature dependence of the rotational collision numbers is in good agreement with the classical calculation of Zeleznik for polar diatomic molecules.