Thermal decomposition of HN(3).

The two-channel thermal decomposition of hydrogen azide, HN(3), was studied computationally. The reaction produces triplet or singlet NH and N(2). A model of the reaction was created on the basis of the theoretical study of the reaction potential-energy surface and microscopic reaction rates by Besora and Harvey (Besora, M.; Harvey, J. N. J. Chem. Phys. 2008, 129, 044303) and the experimental data on the energy-dependent rate constants reported by Foy et al. (Foy, B. R.; Casassa, M. P.; Stephenson, J. C.; King, D. S. J. Chem. Phys. 1990, 92, 2782) The properties of the model were adjusted to fit the calculated k(E) dependence to the experimental one. The experiments on thermal decomposition of HN(3) described in the literature were analyzed via kinetic modeling; the results of the analysis demonstrate that all but one of the existing studies were affected by contributions from secondary kinetics. The model of the reaction was then used in master-equation calculations of the pressure effects and the value of the critical energy transfer parameter, DeltaE(down), was adjusted based on agreement with the experimental k(T,P) data. Finally, the model was used to determine pressure- and temperature-dependent rate constants for both channels of reaction 1, which do not conform to the traditional formalism of low-pressure-limit and falloff description. Uncertainties of the model and their influence on the calculated thermal rate constant values were analyzed. Finally, parametrized expression for rate coefficients were provided for a wide range of temperatures and pressures.