Vibrational relaxation of uranium hexafluoride: Ultrasonic measurements

Ultrasonic attenuation has been measured in UF6 at room temperature over an f/P range of 20 kHz/atm to 70 MHz/atm. A single relaxation process was inferred with an isothermal relaxation time of 5.7 x 10-9 sec-atm. Assuming the three higher energy modes are coupled by fast transfer processes to the three lower energy modes and that the three lower energy modes relax together in parallel, it was found that the rate of de-excitation of the first excited level of the lower energy modes is 4.2 x 10-8 sec-1xatm-1. This corresponds to an average of 17 collisions to transfer a quantum of vibrational energy to translation