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

The homogeneous exchange reaction between tetradeutero methane and ammonia was studied behind reflected shocks in a single-pulse shock tube over the temperature range of 1300–1800°K. The rate of production of CD₃H at the early stages of the reaction in mixtures ranging between 1-4.5% NH₃ and 1–4.3% CD₄ in argon is given by dCD₃H]/dt=k_b CD₄]₀NH₃]₀, where k_b=8 × 10¹⁶ exp (?65.3 × 10³/RT) cm³/mole·sec. This activation energy is considerably lower than the one that may be expected on the basis of a pure free radical mechanism. It is rationalized by C₂D₆ impurities in the methane. No clear answer can be obtained regarding the role of a four-center intermediate in this reaction.