偏二甲肼分解及NO₂脱氢反应速率常数计算

To address the issue of inaccuracies in the kinetic model of the chemical reactions between unsymmetrical dimethylhydrazine and N₂O₄, high-precision quantum chemical calculations of key reactions are conducted. Initially, employing ab initio methods, the rate coefficients for unsymmetrical dimethylhydrazine decomposition and NO₂abstraction reactions are computed. The potential energy surface of the reaction system is determined using the CCSD(T)/ cc-pVTZ//B2PLYPD3/6-311++G(d, p) calculation level. Subsequently, the potential energy surface of barrierless reactions is corrected utilizing the multi-reference state method and the CASPT2/CBS/ / CASPT2/cc-pVTZ calculation level. Finally, temperature and pressure- dependent rate coefficients are obtained employing gas-phase unimolecular reaction theory/master equation theory, and rate coefficients for barrierless reactions are calculated using variational transition state theory. The numerical results demonstrate that the calculated rate coefficients are well aligned with experimental results, with differences in enthalpy of formation not exceeding 4. 18 kj · mol^-1when compared to data from active thermochemical tables and the NIST database, and entropy differences within 2. 09 J · K^-1· mol^-1. The primary routes for unsymmetrical dimethylhydrazine decomposition involve the generation of CH₃+CH₃NNH₂and NH₂+CH₃NCH₃. In the NO₂dehydrogenation reaction, the pathway leading to CH₃(CH₂)NNH₂+ HONO exhibits the highest proportion. Variational transition state theory proves to be more precise in calculating rate coefficients for reactions with low or no barriers than traditional transition state theory, also providing uncertainties across various pressures and temperatures. These research outcomes can provide essential theoretical backing for numerical simulations of rocket engine combustion chambers.