THERMAL-DISSOCIATION RATE OF ETHANE AT THE HIGH-PRESSURE LIMIT FROM 250 TO 2500-K

Experimental measurements of the thermal decomposition rate of ethane from 1330 to 2500 K, extrapolated to high pressure limit rate constants using RRK theory, are found to be in accord with previous work. Combining low temperature methyl radical recombination rate constants with ethane decomposition rate constants results in a coherent set of rate measurements for this process at the high pressure limit from 250 to 2500 K. RRKM calculations using several models for the critical configuration were performed and compared with this data base. A critical configuration model using a minimum density-of-states criterion for defining the critical configuration and a hindered rotor description for the four degrees of freedom that are converted from vibrations in the molecule to free rotations of the methyls was found to give a substantially better description of the data than any vibrator or free rotor model. Since it was not possible to fit the experimental temperature dependence of the high pressure limit recombination rate constant with any critical configuration model, one must conclude either that the minimum-density-of-states version of the RRKM model is incorrect, or that the strong-collision assumption inherent in extrapolating the high temperature decomposition rate data leads to a substantial underestimate of the high pressure limit rate constant. © 1979 American Chemical Society.