A theoretical insight on the exergonic mechanism for Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)

Cyclic nitramine hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a crucial energetic compound widely used in military applications. The thermal decomposition mechanism has attracted considerable interest because of its significance in understanding the sensitivity mechanism of cyclic nitramine materials. While numerous studies of RDX decomposition have focused on the initial unimolecular decomposition and the final products, the exergonic behaviors that could cause reaction growth have garnered limited attention. To gain a clear understanding of the exergonic mechanism during the decomposition of RDX, we performed a theoretical investigation of both unimolecular and bimolecular reactions using density functional theory (DFT). The results indicate that bimolecular reactions play an important role for RDX decomposition. The initial primary small molecule NO₂, acts as a reactive catalyst that triggers the autocatalysis process, facilitating the decomposition of RDX. The main exothermic reactions are the NO₂-autocatalysis reaction and hydrogen abstraction reaction by hydroxyl radicals (OH•). A “reaction loop” is identified that features favorable, exothermic interactions between RDX and the initial reactive species NO₂, HONO, OH•, and NO. This loop accumulates energy and results in the formation of final products such as s-triazine (TAZ) and H₂O.