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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Thermochemical and kinetic analysis of the thermal decomposition of monomethylhydrazine: An elementary reaction mechanism
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Thermochemical and kinetic analysis of the thermal decomposition of monomethylhydrazine: An elementary reaction mechanism

机译：一甲基肼热分解的热化学和动力学分析：基本反应机理

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The reaction kinetics for the thermal decomposition of monomethylhydrazine (MMH) was studied with quantum Rice-Ramsperger-Kassel (QRRK) theory and a master equation analysis for pressure falloff. Thermochemical properties were determined by ab initio and density functional calculations. The entropies, S degrees(298.15 K), and heat capacities, C-p degrees(T) (0 <= T/K <= 1500), from vibrational, translational, and external rotational contributions were calculated using statistical mechanics based on the vibrational frequencies and structures obtained from the density functional study. Potential barriers for internal rotations were calculated at the B3LYP/6-311G(d,p) level, and hindered rotational contributions to S degrees(298.15 K) and C-p degrees(T) were calculated by solving the Schrodinger equation with free rotor wave functions, and the partition coefficients were treated by direct integration over energy levels of the internal rotation potentials. Enthalpies of formation, Delta H-f degrees(298.15 K), for the parent MMH (CH3NHNH2) and its corresponding radicals (CH3NNH2)-N-center dot, (CH3NHNH)-H-center dot, and (CH2NHNH2)-H-center dot were determined to be 21.6, 48.5, 51.1, and 62.8 kcal mol(-1) by use of isodesmic reaction analysis and various ab initio methods. The kinetic analysis of the thermal decomposition, abstraction, and substitution reactions of MMH was performed at the CBS-QB3 level, with those of N-N and C-N bond scissions determined by high level CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) calculations. Rate constants of thermally activated MMH to dissociation products were calculated as functions of pressure and temperature. An elementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literature data was developed to model the experimental data on the overall MMH thermal decomposition rate. The reactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling of MMH homogeneous decomposition at atmospheric conditions.
机译：利用量子莱斯-拉姆斯珀格-卡塞尔（QRRK）理论和压力下降的主方程分析研究了单甲基肼（MMH）热分解的反应动力学。通过从头算和密度函数计算来确定热化学性质。使用统计力学基于振动频率计算出来自振动，平移和外部旋转贡献的熵S度（298.15 K）和热容Cp度（T）（0 <= T / K <= 1500）以及从密度泛函研究获得的结构。在B3LYP / 6-311G（d，p）级别上计算出内部旋转的潜在障碍，并通过使用自由转子波函数求解Schrodinger方程来计算对S度（298.15 K）和Cp度（T）的受阻旋转贡献。 ，并通过内部旋转势能水平上的直接积分来处理分配系数。母体MMH（CH3NHNH2）及其相应的自由基（CH3NNH2）-N-中心点，（CH3NHNH）-H-中心点和（CH2NHNH2）-H-中心点的形成焓Delta Hf度（298.15 K）通过使用等电势反应分析和各种从头算方法确定为21.6、48.5、51.1和62.8 kcal mol（-1）。在CBS-QB3级别上对MMH的热分解，抽象和取代反应进行动力学分析，而NN和CN键的裂解则由高水平CCSD（T）/ 6-311 ++ G（3df， 2p）// MPWB1K / 6-31 + G（d，p）计算。计算热活化的MMH与解离产物的速率常数作为压力和温度的函数。建立了基于计算出的速率常数，热化学性质和文献数据的基本反应机理，以对整体MMH热分解速率的实验数据进行建模。发现N-N和C-N键断裂的反应是模拟大气条件下MMH均相分解的主要反应路径。

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