Thermal decomposition of solid cyclotrimethylene trinitramine

In this paper, we show how a traditional solid-state chemistry approach, applied to the essentially molecular problem of the energetic barrier for decomposition, gives qualitatively new results and, in fact, brings very new perspectives in the detonation initiation theory development at large. Quantum-chemical simulations of the thermal decomposition of solid cyclotrimethylene trinitramine (RDX) by means of the Hartree-Fock method combined with the cluster and periodic models are performed. We found that the dissociation of the RDX molecule in the bulk crystal is characterized by the different energetic barriers for cleavage of N-NO2 bonds, unlike the gas-phase molecule, where all three of the energies are equal. It is also shown that a rupture of the N-NO2 chemical bond requires less energy for an isolated molecule than for a molecule placed in the bulk of the solid. The situation changes if the molecule is close to the free surface of the crystal. In this case, less energy is required to break the bond than for a bulk molecule. Mechanisms of solid RDX decomposition, the relevant experimental data, and possible applications of the results obtained are discussed in great detail. We also discuss how the conclusion obtained can serve for the better understanding of the well-known mechanism of pore collapse, of different sensitivities to detonation initiation of porous, solid, perfect, and defective explosives, and other processes that take place in hot spots. The mechanisms of the thermal decomposition of solid energetic materials are discussed with the illustrating example of RDX.