The thermal decomposition mechanism of energetic cyclopentazolate salt N₂H₅N₅: a deep neural network potential accelerated molecular dynamics study

As a nitrogen-rich metal-free energetic salt, crystalline N₂H₅N₅ with a cyclopentazolate anion has been recently synthesized, but its decomposition mechanism is far from clear. In this study, a neural network potential (NNP) has been developed to investigate the complex reaction dynamics of N₂H₅N₅. Large-scale ab initio-quality molecular-dynamics simulations driven by this model demonstrate that the NNP accurately captures the time-resolved emergence and disappearance of intermediate species in the reaction of the bulk crystal. The triggering event is synchronous: the N₂H₅⁺ cation initiates a step-wise dehydrogenation while the N₅⁻ ring undergoes either (i) direct cleavage or (ii) hydrogen-assisted opening. Once these two “ignition” steps have occurred, the subsequent chemistry is that successive H-stripping from N₂H₅⁺ and rapid rearrangement of the opened N₅⁻ chain lead almost exclusively to the formation of N₂ and NH₃ with only trace amounts of radicals. This simplicity stands in sharp contrast to CHON explosives such as TNT or RDX, where initiation is dominated by nitro-group scission and the ensuing NO₂-driven redox cascade spawns a tangled network of hundreds of intermediates. Furthermore, we have calculated the apparent activation energy of the decomposition of N₂H₅⁺ and N₅⁻, revealing that N₂H₅⁺ is consumed significantly faster than N₅⁻. This work not only clarifies the decomposition mechanism of N₂H₅N₅ but also provides a reliable approach for studying energetic ionic salts, contributing to a deeper understanding of their chemistry.