Vibrational Relaxation of Polyatomic Molecules in Gas Mixtures,
OTTAWA UNIV (ONTARIO) DEPT OF CHEMISTRY
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Experimental measurements were made of the vibrational relaxation rates of CH4 and C2H4 behind shock waves. The laser schlieren technique was used in order to find the rates at temperatures as low as 330 K. The vibrational relaxation times agreed within 5 of other workers ultrasonics measurements of pure ethylene and shock tube measurements of pure methane. Precision of better than 1 for individual mixtures allowed for a sensitive test of the linear mixture rule for methane k sigma xiki where ki are the quasi-first order rate constants for the gas by collider i, xi the mole fraction of the species i in a mixture, and k the overall rate constant for the mixture. It was found that with methane-argon mixtures the linear mixture rule was not strictly obeyed. Distortion from linearity is evident at mole fractions of CH4 0.02, and is most pronounced at the highest temperatures studied 1600 K.