COMPARATIVE ANALYSIS OF DECOMPOSITION REACTIONS IN GASEOUS AND CRYSTALLINE β-HMX

First principles theoretical modeling of decomposition of gas-phase HMX molecules and HMX crystals containing defects is performed by means of density functional theory and transition state theory. A comparative analysis of chemical reactions in a single HMX molecule, a perfect crystalline HMX and the crystal containing free surfaces and molecular vacancies demonstrates that chemical bond dissociations are significantly accelerated for molecules that are placed near a free surface, an internal void, or a vacancy. Our study suggests that main reasons to cause this effect are: (1) The imbalance of intermolecular interactions near defects, (2) The surface-induced reduction of the activation barrier due to outward relaxation of surface NO2 groups, and (3) A large activation volume required for the N-NO2 homolysis reaction, which becomes available near a surface, void, or vacancy.