Vibrational Relaxation in CO2 and CO2–Ar Mixtures Studied Using a Shock Tube and a Laser–Schlieren Technique

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Abstract
Vibrational relaxation has been studied in CO2 and CO2–Ar mixtures over the temperature range 360°–3000°K using a laser–schlieren method. The purpose of this investigation was to compare the results obtained by this technique with those deduced using a Mach–Zehnder interferometer and to provide further evidence as to whether relaxation times depend upon how far the system is from equilibrium as well as on the translational temperature. Relaxation times measured by these two methods agree well. The laser–schlieren method is the more satisfactory for measuring the rate of relaxation and the Mach–Zehnder for finding the total density change during the process. These new results support the view that relaxation times do not depend upon how far the system is from equilibrium. The measurements using CO2 and CO2–Ar mixtures show that CO2 is about five times as effective as Ar in causing relaxation at 360°K and two times as effective at 2000°K.