Ultrasonic Determination of Rotational Collision Numbers and Vibrational Relaxation Times of Polyatomic Gases at High Temperatures

Abstract

An ultrasonic method has been used in experimentally determining the rotational collision numbers, and vibrational relaxation times of polyatomic gases at high temperatures. An ultrasonic (∼1–3 MHz) pulse method has been used to measure both sound velocity and sound absorption in nitrogen, oxygen, and carbon dioxide in the temperature range of 300°—1300°K. All of the measurements were obtained at a pressure of one atmosphere. Vibrational relaxation times of carbon dioxide have been determined from the sound absorption measurements from 300° to 1300°K. Rotational collision numbers have been obtained as a function of temperature in oxygen and nitrogen and are in reasonable agreement with the theoretical values given by Parker. This agreement has established that the transport properties of nondissociated diatomic molecules (homonuclear) can also be determined from ultrasonic measurements.