Isomerization and reaction process of N(2)O(4)(H(2)O)(n)

Liquid propellant N(2)O(4) is prone to absorb H(2)O to form an N(2)O(4)(H(2)O)(n) system during long-term storage, ultimately generating HNO(3), HNO(2), 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 N(2)O(4)(H(2)O)(n) 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 H(2)O in the N(2)O(4)(H(2)O)(n) 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-ONONO(2) group and the ON–ONO(2) 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 NO(3)(−) to NO(+), making the ON–ONO(2) bond less susceptible to cleavage, further verifying that N(2)O(4)(H(2)O)(n) tends to afford the products directly in one step as H(2)O accumulates in the system.