Interpreting
the initial decomposition mechanism is important for
evaluating the thermal stability of explosives. In this study, we
theoretically investigated the initial thermal decomposition reactions
for two typical energetic materials, FOX-7 and RDX, in both the gas
phase and crystal phase. Single molecular decomposition pathways in
the gas phase are calculated using the density functional theory (DFT)
method, and the crystal phase reactions are simulated through the
MM/DFT-based ONIOM method. The calculation results indicate that the
crystal environment has a significant influence on the initial thermal
decomposition mechanism of FOX-7 and RDX. The cage effect induced
by the crystal environment greatly confines molecular mobility and
diffusion, rendering the generated small molecules to react with the
remaining fragment and yield new decomposition channels compared with
the gas phase condition. The crystal packing structures and intermolecular
interactions (hydrogen bonds/π–π stacking) significantly
increase the reaction barriers of FOX-7 and RDX, leading to the crystal
phase reactions being more difficult to occur than in the gas phase.
Since the practical application of explosives is mostly in the crystal
state, it is important to consider the environmental effects on the
initial decomposition reactions. The same insight can also be relevant
for other energetic materials.
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