Direct dynamics study on the hydrogen abstraction reaction N ₂H₄ + H → N₂H₃ + H₂

A direct ab initio dynamics method has been employed to investigate the hydrogen abstraction reaction N₂H₄ + H → N ₂H₃ + H₂, which is predicted to have four possible reaction channels caused by different structures of N₂H ₄ and different positions of hydrogen atom attack. The structures and frequencies at the stationary points and along the minimum energy paths (MEPs) are determined using the UMP2/6-31+G(d,p) method. Energetic information is further refined at the PMP4/6-311+G(3df,2pd)//UMP2/6-31+G(d,p) level of theory. The rate constants are calculated using the improved canonical variational transition state theory with the small-curvature tunneling correction (ICVT/SCT) in the temperature range of 220-3000 K. The calculated results show that in the lower-temperature range, the most favorable reaction channels are reaction 1 [N₂H₄(a) + H → TS(al) → N₂H₃(a) + H₂] and reaction 3 [N ₂H₄(b) + H → TS(b1) → N₂H ₃(b) + H₂], while in the higher-temperature range, reaction 2 [N₂H₄(a) + H → TS(a2) + N ₂H₃(a) + H₂] and reaction 4 [N ₂H₄(b) + H → TS(b2) → N₂H ₃(b) + H₂] become more important. The calculated total rate constants of the four reaction channels are in good agreement with the available experimental data.