Ultrasonic Absorption in Gaseous Methane

The ultrasonic absorption of methane has been measured in the frequency/pressure range from 50 kHz/at to 600 kHz/at, at temperatures between −30 °C and +120 °C. The maximum of the molecular absorption caused by vibrational relaxation is observed in this frequency/pressure range. The measurements have been performed with an arrangement of two equal electrostatic transducers (of the Sell-type) as transmitter and receiver. Relaxation times and impact rates are calculated from the experimenal absorption plots and are compared with results obtained by other authors. The peak value of the absorption coefficient is higher than to be expected from the conventional calculation of the vibrational specific heat.