Comparative study on the thermal decomposition of structural isomers: Pyrazole and imidazole energetic materials

Exploration of the thermal decay mechanisms of energetic skeletons supports the understanding of stability and energy release. Herein, we comparatively investigated the thermal decomposition of energetic isomers nitropyrazole and nitroimidazoles at high temperature and high density based on ReaxFF-lg reactive molecular dynamics simulations, which have not been fully understood. Results show that the initial decomposition reaction of nitropyrazole and nitroimidazole were triggered by the OH elimination as a result of intermolecular H-shift. And the N₂ elimination plays a major role in the decomposition of pyrazoles, while the formation of hydrogen cyanide CHN is the main decomposition channel of imidazoles. Another important channel of their nitro derivatives is C-NO₂ bond dissociation. At high density, the cleavage of C-NO₂ bonds is inhibited, and the reactions between molecules are promoted, therefore the dimers are easier to produce. Detailed evolution yields of key intermediates, final gaseous products, and clusters are also presented to study the difference in the thermal decay of pyrazoles and imidazoles, as well as the effect of pressure. Overall, these thermolysis properties of nitropyrazole and nitroimidazole are expected to gain more knowledge to the diversity of thermal decomposition of energetic isomers.