Thermal Decomposition of HN₃

Abstract

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.

Reactive Force Field for Liquid Hydrazoic Acid with Applications to Detonation Chemistry

“…The thermal decomposition of HN 3 has been studied in the past both experimentally , and computationally. , The experimental efforts were limited to dilute HN 3 in argon, thus, the applicability of their results is limited to the gas phase. In accordance with our DFT calculations, the more favorable unimolecular decomposition channel, namely, the one with the lowest barrier (Δ E r = 16.39 kcal/mol) is the spin-forbidden channel forming the triplet 3 NH, in agreement with literature. , ReaxFF HN3 was trained to reproduce the energy barrier of the lowest energy route (i.e., the spin-forbidden channel).…”

“…The thermal decomposition of HN 3 has been studied in the past both experimentally , and computationally. , The experimental efforts were limited to dilute HN 3 in argon, thus, the applicability of their results is limited to the gas phase. In accordance with our DFT calculations, the more favorable unimolecular decomposition channel, namely, the one with the lowest barrier (Δ E r = 16.39 kcal/mol) is the spin-forbidden channel forming the triplet 3 NH, in agreement with literature. , ReaxFF HN3 was trained to reproduce the energy barrier of the lowest energy route (i.e., the spin-forbidden channel). Kajimoto et al and Knyazev et al analyzed the kinetics of secondary reactions in shock tube experiments and identified several possible decomposition and recombination reactions.…”

“…The thermal decomposition of HN 3 has been studied in the past both experimentally 14,5 and computationally. 6,7 The experimental efforts were limited to dilute HN 3 in argon, thus, the applicability of their results is limited to the gas phase.…”

“…5,14 ReaxFF HN3 was trained to reproduce the energy barrier of the lowest energy route (i.e., the spin-forbidden channel). Kajimoto et al 14 and Knyazev et al 5 analyzed the kinetics of secondary reactions in shock tube experiments and identified several possible decomposition and recombination reactions. Some of the key reactions in Figure 5 are based on their suggestions.…”

“…Nevertheless, it was demonstrated that HN 3 can be desensitized sufficiently in aqueous solutions so as to be safe to handle while still considered to be highly explosive . Owing to its simple molecular structure, HN 3 can serve as a model liquid system to study material properties and behavior under extreme conditions such as during detonation. − In addition, HN 3 is the simplest template for more complex systems such as organic azides. − Due to the existence of conjugated NNN bonds in the molecule, it is tempting to claim that polymerization and subsequent transition to a nonmolecular and even a metallic state may be possible following high pressure loading . Although it was first synthesized in 1890, its crystal structure has only recently been determined experimentally and shows a unique network of hydrogen bonds .…”