Multiple vibrational relaxation in polyatomic gases and mixtures
Abstract
Ultrasonic dispersion measurements have been made in gaseous C2N2 and CF3CN at 294 K. Both molecules show two vibrational relaxation times. The measured values are compared with calculations based on the SSH-Tanczos quantum-mechanical theory. Calculated relaxation times are in fair agreement with experiment for vibration-translation transfer from lowest molecular modes, but the theory consistently underestimates the probability of complex intramolecular vibration-vibration transfer from upper modes. The experimental collision numbers for intramolecular vibration-vibration transfer are discussed in relation to other data available for both intramolecular and intermolecular transfers.
Dispersion measurements have also been made in mixtures of the doubly relaxing gas, SO2, with the singly relaxing gas, CH2F2. The mixtures show a single relaxation time for the whole vibrational energy content of both molecules. This is interpreted as due to rapid near-resonant vibration-vibration transfer between upper modes of the two molecules, which enables the CH2F2 to act as an energy-transfer catalyst.