A quantum mechanics study on early decomposition reactions for liquid-phase HMX

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, (HMX), also known as octogen, is a commonly used ingredient in solid propellants and explosives. As a result, HMX has been the subject of many experimental and theoretical investigations to elucidate its liquid-phase and gas-phase decomposition behavior. In various experimental efforts, including both fast and slow thermolysis, the results indicate that ring-opening occurs very early due to the presence of carbon-containing species, such as HCN, H2CO, HNCO, CO and CO2. After a lengthy search using quantum mechanics, ring-opening and subsequent reactions have been identified. These ring-opening and subsequent reactions may occur in both liquid and gas phases. The quantum mechanics investigation is based on using density functional theory. The liquid-phase studies use the CPCM solvation model with water as solvent within the Gaussian 09 program package. Intrinsic reaction coordinate calculations have also been performed to verify that the reactants indeed are connected to the expected products. Similar to RDX, HONO elimination appears to be the initiation reaction. Competing bimolecular reactions with NO2 and ONNO2 are also investigated in the liquid phase. Similar reactions with other species such as O2NNO2, NO and HONO are likely to play an important role and need to be further investigated.