The vibrational energy rate of approach to thermal equilibrium of suddenly heated CO2gas has been studied by using a shock tube and the integrated schlieren method for density measurements. The experimental results agree fairly well with the predicted direct excitation of bending mode and indirect excitation of valence mode in the temperature range 440deg;mdash;816deg;K. The measured relaxation times for the direct excitation process range from 3.75 mgr;sec at 440deg;K to 0.64 mgr;sec at 816deg;K. The effects of impurities through leakage in the tube can be considered negligible. The average temperatures of the measured bending energies are slightly higher than the corresponding temperatures of the valence energies, which indicates that the time constant of the indirect excitation process is at least one order of magnitude smaller.
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