Systematically Exploring Decomposition Routes of HMX Explosive Molecule

This investigation performs three quantum chemical calculations to determine an unrealizable profile of the HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) unimolecular decomposition. First, the bonding energies of HMX and its corresponding decomposition species were calculated using the differential over lap (INDO) program, which identifies the weak est bonding site for reference and determines the site of easiest cleavage. Second, the molecular energies of all species were estimated by performing density-functional theory (DFT) calculations, yielding an accurate enthalpy of formation following calibration according to a five-parametric equation. Finally, all decomposition transition states were sought using Quasi-Newton and Synchronous Transit approaches (QST3 procedure). Computational results reveal that the activation energy of direct cis-form HONO elimination is lower than that of direct trans-form HONO elimination and that of the two-stage elimination of two forms of HONO (N-N bond fission combined with C-H bond breaking) in the initial decomposition step, which are 234.7 kJ/mol and 147.9-171.4 kJ/mol, respectively.