Thermochemical and Kinetic Analysis of the Thermal Decomposition of Monomethylhydrazine: An Elementary Reaction Mechanism
详细信息 查看全文
- 作者：Hongyan Sun ; Chung K. Law
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：May 17, 2007
- 年：2007
- 卷：111
- 期：19
- 页码：3748 - 3760
- 全文大小：445K
- 年卷期：v.111,no.19(May 17, 2007)
- ISSN：1520-5215
文摘
The reaction kinetics for the thermal decomposition of monomethylhydrazine (MMH) was studied with quantumRice-Ramsperger-Kassel (QRRK) theory and a master equation analysis for pressure falloff. Thermochemicalproperties were determined by ab initio and density functional calculations. The entropies, S
(298.15 K), andheat capacities, Cp(T) (0 
T/K 1500), from vibrational, translational, and external rotational contributionswere calculated using statistical mechanics based on the vibrational frequencies and structures obtained fromthe density functional study. Potential barriers for internal rotations were calculated at the B3LYP/6-311G(d,p) level, and hindered rotational contributions to S(298.15 K) and Cp(T) were calculated by solving theSchrödinger equation with free rotor wave functions, and the partition coefficients were treated by directintegration over energy levels of the internal rotation potentials. Enthalpies of formation, 
fH(298.15 K),for the parent MMH (CH3NHNH2) and its corresponding radicals CH3N
NH2, CH3NHNH, and CH2NHNH2were determined to be 21.6, 48.5, 51.1, and 62.8 kcal mol-1 by use of isodesmic reaction analysis and variousab initio methods. The kinetic analysis of the thermal decomposition, abstraction, and substitution reactionsof MMH was performed at the CBS-QB3 level, with those of N-N and C-N bond scissions determined byhigh level CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) calculations. Rate constants of thermallyactivated MMH to dissociation products were calculated as functions of pressure and temperature. Anelementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literaturedata was developed to model the experimental data on the overall MMH thermal decomposition rate. Thereactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling ofMMH homogeneous decomposition at atmospheric conditions.
(298.15 K), andheat capacities, Cp(T) (0 T/K 1500), from vibrational, translational, and external rotational contributionswere calculated using statistical mechanics based on the vibrational frequencies and structures obtained fromthe density functional study. Potential barriers for internal rotations were calculated at the B3LYP/6-311G(d,p) level, and hindered rotational contributions to S(298.15 K) and Cp(T) were calculated by solving theSchrödinger equation with free rotor wave functions, and the partition coefficients were treated by directintegration over energy levels of the internal rotation potentials. Enthalpies of formation, fH(298.15 K),for the parent MMH (CH3NHNH2) and its corresponding radicals CH3NNH2, CH3NHNH, and CH2NHNH2were determined to be 21.6, 48.5, 51.1, and 62.8 kcal mol-1 by use of isodesmic reaction analysis and variousab initio methods. The kinetic analysis of the thermal decomposition, abstraction, and substitution reactionsof MMH was performed at the CBS-QB3 level, with those of N-N and C-N bond scissions determined byhigh level CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) calculations. Rate constants of thermallyactivated MMH to dissociation products were calculated as functions of pressure and temperature. Anelementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literaturedata was developed to model the experimental data on the overall MMH thermal decomposition rate. Thereactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling ofMMH homogeneous decomposition at atmospheric conditions.