NO₃ radical is known as a dominant oxidant in the atmosphere at night, and plays an important role in atmospheric chemistry. Recently, NO₃ radical is reported to be formed in the decomposition process of RDX, while it has never been detected in experiment up to now. The possible reason is that it would react with RDX or some RDX decomposition products once it is formed. This study for the first time theoretically investigated the bimolecular reactions of NO₃ radical with two kinds of decomposition products of RDX (HNO and HONO) by computational chemistry methods, and the reaction mechanisms are studied using CCSD(T)/6-311++G(d,p) theoretical methods based on the geometric parameters optimized at the B3LYP/6-311++G(d,p) level. Same mechanisms are devised for the two reactions, such as oxygen abstraction and hydrogen abstraction. The two kinds of reaction pathways are of equal importance for the two reactions, because of similar barrier heights obtained in this study. The two pathways of the reation of NO₃+HNO can result in two kinds of products HNO₂+NO₂ and HNO₃+NO respectively, while the reaction of NO₃+HONO only yields HNO₃+NO₂. The two reactions proceed with low barrier heights (0～0.5 kcal/mol, and 15.9～18.5 kcal/mol respectively), which are significantly lower than that of the reactions of RDX decomposition and NO₃ formation. Moreover, the results show that the reaction of NO₃ radical with HNO is barrierless and exothermic, implying it is energetically feasible to take place. The reaction may be responsible for the disappearance of NO₃ radical during the decomposition process of RDX. Moreover, the isomerization reactions of HNO and HONO are also investigated by using the same methods, and a hydrogen atom intramolecular migration mechanism is found for these two isomerization reactions. The study is a necessary precursor for providing parameters for subsequent kinetic study and encourages further experimental investigation in future.

Key words: NO₃, HNO, HONO, reaction mechanism