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.