Decontamination of organic pollutants by plasma is a novel advanced oxidation process, in which ·OH is believed to play a crucial role, and it’s potential to be applied in the degradation of wastewater containing unsymmetrical dimethylhydrazine (UDMH). However, the chemical kinetics of UDMH decompose still remain unclear which makes UDMH degradation by plasma a lack of theoretical basis, so the chemical kinetics of UDMH with ·OH should be studied. In this paper, the decomposition mechanism of UDMH with ·OH was investigated theoretically based on density functional theory (DFT). The calculation level adopted in this paper is M06-2X/6-31G* method in a solvation model based on solute electron density (SMD). Reaction of UDMH + ·OH → (CH₃)₂NNH (UDMHr) + H₂O was first studied and compared in both aqueous solution and gaseous phase to reveal the necessity of considering solvent, and the results showed that solvent has non-negligible effect in aqueous reaction mechanism to improve the accuracy of rate constant. Then, six potential reactions were found in UDMH + ·OH decomposition pathways in aqueous solution and a two-step calculation procedure was adopted to guarantee the accuracy of free energy. Based on the calculated rate constants, UDMHr, (CH₃)CH₂NNH₂, dimethylamino and CH₃NNH₂ were selected as the precursors of subsequent byproducts of N-nitrosodimethylamine, methylhydrazine, nitromethane, formaldehyde hydrazone and dimethyldiazene. And methanol and hydroxylamine were sorted into critical byproducts of UDMH + ·OH. The potential transformation pathways of main decomposition byproducts were also summarized. The work is a pilot study for subsequent theoretical plasma modeling and experiments.

等离子体净化有机污染物是一种新型的高级氧化工艺，其中·OH在其中发挥着至关重要的作用，在含不对称二甲肼（UDMH）废水的降解中具有应用潜力。然而，UDMH分解的化学动力学仍不清楚，这使得等离子体降解UDMH缺乏理论依据，因此应研究UDMH与·OH的化学动力学。本文基于密度泛函理论（DFT）从理论上研究了UDMH与·OH的分解机理。本文采用的计算水平是基于溶质电子密度（SMD）的溶剂化模型中的M06-2X/6-31G*方法。UDMH + ·OH → (CH ₃ ) ₂ NNH (UDMHr) + H _2的反应首先对O在水溶液和气相中进行了研究和比较，以揭示考虑溶剂的必要性，结果表明溶剂在水反应机理中对提高速率常数的准确性具有不可忽略的作用。然后，在水溶液中的UDMH+·OH分解途径中发现了六个潜在反应，并采用两步计算程序来保证自由能的准确性。基于计算的速率常数，UDMHr、(CH ₃ )CH ₂ NNH ₂、二甲氨基和CH ₃ NNH ₂被选为N后续副产物的前体。-亚硝基二甲胺、甲基肼、硝基甲烷、甲醛腙和二甲基二氮烯。甲醇和羟胺被分选为UDMH + ·OH 的关键副产物。还总结了主要分解副产物的潜在转化途径。这项工作是后续理论等离子体建模和实验的初步研究。