Kinetics of the Homogeneous Exchange Reaction: NH3 +D2→NH2D +HD. Single-Pulse Shock-Tube Studies

The homogeneous exchange reaction between ammonia and deuterium was studied in a single-pulse shock tube over a wide range of compositions and initial pressures within the 1150–1450°K temperature range. The rate of production of HD in the early stages of the reaction, in the composition range 0.67–4% NH3 and 0.67–4% D2 in argon is given by d[HD]/dt = kb[Ar]0.38[NH3]0.61[D2]1.01, where kb = 1013.0 ± 0.3exp[−(37.2 ± 1.0) × 103/RT]cc mole−1·sec−1. The contribution of a chain mechanism to the exchange process was ruled out. A mechanism based on vibrational excitation of the deuterium molecule to a critical vibration level as a slow step prior to the atom switching step is proposed.