Self-Accelerated Mechanochemistry in Nitroarenes

The initiation of explosive decomposition in two energetic crystals, diamino−dinitroethylene (DADNE, C2H4N4O4) and triamino−trinitrobenzene (TATB, C6H6N6O6), was investigated using density functional theory. The initial chemical reactions in ideal TATB crystals were found to be determined by three main decomposition mechanisms that are almost unaffected by a shear-strain-induced deformation, C−NO2 homolysis, nitro−nitrite isomerization, and proton transfer. The two latter reactions are nearly isoenergetic and have lower activation energies than the first reaction. At the same time, decomposition of DADNE is found to depend strongly on the molecular environment; molecules in ideal DADNE crystals favor nitro−nitrite isomerization, while molecules located at shear planes decompose via the C−NO2 homolysis pathway. We also established that the shear-strain accumulated in the DADNE dashboard-shaped molecular layers triggers an exothermic regime at fairly early stages of decomposition. In contrast, the structure of TATB that consists of flat, graphite-like molecular layers activates accelerated exothermal chemistry only at much higher concentrations of initial decomposition products.