A shock tube study of vibrational relaxation in pure CO2 and mixtures of CO2 with the inert gases, nitrogen, deuterium and hydrogen

Abstract

Abstract Vibrational relaxation times have been measured in CO2 and CO2 mixtures from 360 to 1500 K by a laser-schlieren method. The scatter in the results is small and there is excellent agreement with recent ultrasonic measurements. Within the experimental error the relaxation times for a given pressure are a function of the translational temperature alone and do not depend upon how close the system is to equilibrium. Simple theories of vibrational relaxation do not account for the results satisfactorily. This applies particularly to the temperature coefficients of the relaxation times of CO2 relaxed by H2 and D2. In general it seems that above 1000 K the relaxation time may be controlled largely by the reduced mass of the collision partners while at lower temperatures this may be true for the inert gases, but not for other molecules.