Vibrational Relaxation Measurements of Carbon Monoxide in a Shock-Tube Expansion Wave

A novel technique has been developed for use in the study of collisional energy transfer and chemical reaction rates in rapidly cooled gases. The principal feature is that the shock heated test gas sample is stationary during the cooling process so that the temporal behavior of a particular nonequilibrium property may be continuously monitored. The technique has been applied to the measurement of the vibrational de-excitation rate of carbon monoxide in an argon heat bath, using the fundamental infrared emission band of CO to follow its vibrational temperature throughout the expansion. In contrast to some recent investigations which indicate enhanced vibrational de-excitation rates, the present experiments show that when translation–vibration collisions control the relaxation process the characteristic vibrational relaxation time of carbon monoxide diluted in argon is the same no matter whether it is measured in a compression (shock wave) or expansion environment.