2,6-bis(picrylamino)-3,5-dinitropyridine (PYX) has excellent thermostability, which makes its thermal decomposition mechanism receive much attention. In this paper, the mechanism of PYX thermal decomposition was investigated thoroughly by the ReaxFF-lg force field combined with DFT-B3LYP(6–311++G) method. The detailed decomposition mechanism, small-molecule product evolution, and cluster evolution of PYX were mainly analyzed. In the initial stage of decomposition, the intramolecular hydrogen transfer reaction and the formation of dimerized clusters are earlier than the denitration reaction. With the progress of the reaction, one side of the bitter amino group is removed from the pyridine ring, and then the pyridine ring is cleaved. The final products produced in the thermal decomposition process are CO, HO, N, and H. Among them, HO has the earliest generation time, and the reaction rate constant () is the largest. Many clusters are formed during the decomposition of PYX, and the formation, aggregation, and decomposition of these clusters are strongly affected by temperature. At low temperatures (2500 K–2750 K), many clusters are formed. At high temperatures (2750 K–3250 K), the clusters aggregate to form larger clusters. At 3500 K, the large clusters decompose and become small. In the late stage of the reaction, H and N in the clusters escaped almost entirely, but more O was trapped in the clusters, which affected the auto-oxidation process of PYX. PYX’s initial decomposition activation energy () was calculated to be 126.58 kJ/mol. This work contributes to a theoretical understanding of PYX’s entire thermal decomposition process.

中文翻译：

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反应分子动力学洞察2,6-双(三硝基氨基)-3,5-二硝基吡啶的热分解机理

2,6-双(三硝基氨基)-3,5-二硝基吡啶(PYX)具有优异的热稳定性，这使其热分解机理备受关注。本文利用ReaxFF-lg力场结合DFT-B3LYP(6–311++G)方法对PYX热分解机理进行了深入研究。主要分析了PYX的详细分解机理、小分子产物演化和簇演化。在分解初期，分子内氢转移反应和二聚簇的形成早于脱硝反应。随着反应的进行，吡啶环一侧的苦氨基脱去，然后吡啶环断裂。热分解过程中产生的最终产物为CO、H2O、N和H。其中H2O的生成时间最早，反应速率常数()最大。 PYX分解过程中形成许多团簇，这些团簇的形成、聚集和分解受温度的强烈影响。在低温（2500 K–2750 K）下，会形成许多簇。在高温（2750 K–3250 K）下，团簇聚集形成更大的团簇。在 3500 K 时，大团簇分解并变小。在反应后期，团簇中的H和N几乎全部逃逸，但更多的O被困在团簇中，影响了PYX的自氧化过程。 PYX的初始分解活化能为()计算为126.58 kJ/mol。这项工作有助于从理论上理解 PYX 的整个热分解过程。