Direct ab initio dynamics studies of N + H2<-->NH + H reaction

Kinetics of the N+H2<-->NH+H reaction have been studied using a direct ab initio dynamics method. Potential energy surface for low electronic states have been explored at the QCISD/ cc-pVDZ level of theory. We found the ground-state reaction is N(4S)+H2-->NH(3Σ-)+H. Thermal rate constants for this reaction were calculated using the microcanonical variational transition state theory. Reaction path information was calculated at the QCISD/cc-pVDZ level of theory. Energies along the minimum energy path (MEP) were then refined at the QCISD(TQ)/ cc-pVTZ level of theory. The forward and reverse barriers of the ground-state reaction are predicted to be 29.60 and 0.53 kcal/mol, respectively. The calculated rate constants for both forward and reverse reactions are in good agreement with available experimental data. They can be expressed as k(T)52.3331014 exp(230.83 (kcal/mol)/RT) cm3 mols-1 s-1 for the forward reaction and k(T) 55.553108T1.44 exp(20.78(kcal/mol)/RT) cm3 mol-1 s-1 for the reverse reaction in the temperature range 400-2500 K.