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

Abstract

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 $\mathrm{d[}\mathrm{HD}{\mathrm{]/dt\hspace{0.17em}=\hspace{0.17em}k}}_b[\mathrm{Ar}{]}^{\text{0.38}}[{\mathrm{NH}}_3{]}^{\text{0.61}}[{\mathrm{D}}_2\text{]1.01}$ , where $k_b{\text{\hspace{0.17em}=\hspace{0.17em}10}}^{\text{13.0\hspace{0.17em}±\hspace{0.17em}0.3}}\exp {\text{[−(37.2\hspace{0.17em}±\hspace{0.17em}1.0)\hspace{0.17em}×\hspace{0.17em}10}}^3\mathrm{/RT]}{\mathrm{cc\; mole}}^{\text{−1}}·{\sec }^{\text{−1}}$ . 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.