Computational study of unimolecular decomposition mechanism of RDX explosive

This study investigated the RDX (1,3,5-Trinitro-1,3,5-triazine) molecule to elucidate its possible decomposition species and the corresponding energies by performing the density-functional theory (DFT) calculations. Reasonable decomposition mechanisms are proposed based on the bond energy calculated using the differential overlap (INDO) program, which yields the weakest bonding site for reference and determines the site of easy cleavage. Computational results indicate that the activation energy of direct cis-form HONO elimination is lower than that of direct trans-form HONO elimination and that of a 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 213.9 kJ/mol and 93.8-101.8 kJ/mol, respectively. Two possible pathways are proposed; (1) N-N bond homolytic cleavage followed by elimination of cis-form HONO, and (2) N-N bond homolytic cleavage followed by elimination of trans-form HONO.