A Reevaluation of Low Temperature Experimental Rate Data for the Reactions of O Atoms with Methane, Ethane, and Neopentane

The experimental data for the reactions of oxygen atoms with methane, ethane, and neopentane at temperatures below ca. 600 K have been reexamined. In the case of CH4 and C2H6 reactions, detailed computer models have been assembled to test the assumptions regarding stoichiometries that were made in the original studies in order to derive elementary rate coefficients from the experimentally observed reaction rates. It was found in both cases that the measurements are especially sensitive to secondary reactions not taken into account and impurities in the reagent alkane. Because the original reports did not include sufficient experimental details, it is not now possible to correct their results quantitatively. However, it appears, qualitatively, that the values for the O + CH4 and O + C2H6 rate coefficients were overestimated by factors of approximately 2 to 3 in the 250–400 K temperature range, with the error increasing as T decreases. Although the experimental results for the O + neopentane reaction are not as sensitive to the same kinds of complications, a comparison of the low-temperature measurements with those for the O + ethane reaction suggests that the previously recommended rate coefficients, based on the data of Herron and Huie, are probably also too high by a factor of 2 to 3.