Homogeneous Exchange Reaction: CD4+CH4→CD3H+CH3D. Single Pulse Shock Tube Studies

Abstract

The homogeneous exchange reaction between CH4 and CD4 was investigated using the single pulse shock tube technique. The temperature range covered was 1340–1745°, and concentrations up to 8% total methane in argon were used. The over-all rate of exchange is proportional to the 32 power of the methane concentration and is independent of the argon density. The rate of exchange in mixtures containing 4% CH4 + 1% CD4 and 4% CD4 + 1% CH4 was found to be the same, indicating a negligible isotope effect at the temperature range covered in this study. For mixtures in which [CH4] = [CD4] the rate of exchange is given by d[CD3H] / dt = kr[CH4]0.75[CD4]0.75, where kr = 4.3 × 1014exp[−(70 ± 2) × 103 / RT]cc0.5mole−0.5·sec−1. It was shown that the exchange proceeds via a chain reaction mechanism carried by CH3 and CD3 free radicals. The evaluated rate constants for the chain, CH3+CD4→ lim k3CD3+CH3D, CD3+CH4→ lim k4CH3+CD3H, are by a factor of 10 higher than the ones extrapolated from the low temperature studies on the basis of an Arrhenius plot.

The thermal decomposition of methane. III. Methyl radical exchange in CH4–CD4 mixtures

“…efficient H-D exchange was occurring, much The methyl radical exchange reaction in faster than the decomposition itself, which mixtures of CH, and CD, was studied some closely followed the simple stoichiometry years ago by Burcat and Lifshitz (9) using a CH4 + CD4 + CH3D + CD3H shock tube in the temperature range 1340-1745 1(. They concluded that the exchange The present paper describes kinetic measureproceeded through a methyl-radical chain ments of this exchange reaction in the static pyrolysis system at temperatures from 880 to with the earlier results of Burcat and Lifshitz (9) and confirm their observation of nonArrhenius behaviour in this reaction.…”

“…The two lines shown in Fig. 3 (9) which appear to be representative of their measurements. These authors did not report values of k, directly, but values are implicit in their comparison with low-temperature data.…”

The homogeneous reaction CD4 + NH3 → CD3H + NH2D: The effect of ethane impurities

“…Burcat and Lifshitz [6] suggested some time ago a free radical mechanism to They explain their observations in the exchange reaction between CD, and CH,. found an overall power dependence of 3/2 and no effect of argon on the reaction rate.…”

“…Relatively little effort has been devoted to exchange studies between two polyatomic molecules. Burcat and Lifshitz [6] studied the reaction between CDr and CH4. They found an overall power dependence of 3/2 and concluded that the exchange took place via a free radical mechanism.…”

Ideal Gas Thermodynamic Properties of CH3, CD3, CD4, C2D2, C2D4, C2D6, C2H6, CH3N2CH3, and CD3N2CD3

“…Tabulated Thermodynamic Properties of C 2 H 6 and C;lD 6 Deuterated compounds have been used in studies of hydrocarbon reactions in our laboratory [1]1 and elsewhere [2,3], but there has been no compilation of thermodynamic properties for most of these compounds. The substances which we have included in thi:3 paper are one:3 of broad intere~t for which molecular data are available for calculating accurate thermodynamic properties.…”