Isomerization and reaction process of N₂O₄(H₂O)

Liquid propellant N₂O₄ is prone to absorb H₂O to form an N₂O₄(H₂O) system during long-term storage, ultimately generating HNO₃, HNO₂, and other substances capable of corroding the storage tank, which will adversely affect the performance of weapons and equipment. In this work, the reaction process of the N₂O₄(H₂O) system is simulated using density functional theory, and the potential energy surface, the geometric configurations of the molecules, the charge distribution, and the bond parameters of the reaction course at n = 0-3 are analyzed. The results show that the potential energy of the system is lower and the structure is more stable when the H₂O in the N₂O₄(H₂O) system is distributed on the same side. When n = 1 or 2, the reaction profiles are similar, and the systems are partly ionic, although still mainly covalently bonded. When n = 3, the charge on the trans-ONONO₂ group and the ON-ONO₂ bond length change abruptly to -0.503 a.u. and 2.57 Å, respectively, at which point the system is dominated by ionic bonds. At n = 2, a proton-transfer phenomenon occurs in the reaction course, with partial reverse charge-transfer from NO₃ ^- to NO⁺, making the ON-ONO₂ bond less susceptible to cleavage, further verifying that N₂O₄(H₂O) tends to afford the products directly in one step as H₂O accumulates in the system.