Vibrational Relaxation Times of a Number of Polyatomic Gases Derived from Measurements of Acoustic Absorption

The authors have described in a previous paper a method for deriving the acoustic absorption coefficient of gases from measurements of the decay time of a cylindrical resonator containing the gas in question. This technique has been applied to determine the relaxational contribution to the absorption at frequencies well below the dispersion region for a number of gases. The information is then used to evaluate the relaxation times for deactivation of the vibrational energy and results are given for boron trifluoride, cyclopropane, methane, methyl chloride, carbon tetrafluoride, ethylene, acetylene, 1,3- butadiene and 1,2- dichlorotetrafluoroethane. Agreement is found with relaxation times evaluated from ultrasonic velocity measurements in cases where comparison can be made.