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Theoretical Study of Isomerization and Decomposition Reactions for Methyl-nitramine
Wen-mei Wei ,Ren-hui Zheng ,Yan Tian ,Tian-jing He* ,Li He ,Dong-ming Chen ,Fan-chen Liu
Author NameAffiliation
Wen-mei Wei Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China 
Ren-hui Zheng Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China 
Yan Tian Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China 
Tian-jing He* Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China 
Li He Department of Electronic Science and Technology, University of Science and Technology of China, Hefei 230026, China 
Dong-ming Chen Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China 
Fan-chen Liu Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China 
Abstract:
The complex potential energy surface and reaction mechanisms for the unimolecular isomerization and decomposition of methyl-nitramine (CH3NHNO2) were theoretically probed at the QCISD(T)/6-311+G*//B3LYP/6-311+G* level of theory. The results demonstrated that there are four low-lying energy channels: (i) the N{N bond fission pathway; (ii) a sequence of isomerization reactions via CH3NN(OH)O; (IS2a); (iii) the HONO elimination pathway; (iv) the isomerization and the dissociation reactions via CH3NHONO (IS3). The rate constants of each initial step (rate-determining step) for these channels were calculated using the canonical transition state theory. The Arrhenius expressions of the channels over the temperature range 298-2000 K are k6(T)=1014:8e-46:0=RT , k7(T)=1013:7e-42:1=RT , k8(T)=1013:6e-51:8=RT and k9(T)=1015:6e-54:3=RT s-1, respectively. The calculated overall rate constants is 6.9£10-4 at 543 K, which is in good agreement with the experimental data. Based on the analysis of the rate constants, the dominant pathway is the isomerization reaction to form CH3NN(OH)O at low temperatures, while the N{N bond fission and the isomerization reaction to produce CH3NHONO are expected to be competitive with the isomerization reaction to form CH3NN(OH)O at high temperatures.
Key words:  Methyl-nitramine, Potential energy surface, Reaction mechanism, Canonical transition state theory, Rate constant
FundProject:This work was supported by the National Natural Science Foundation of China (No.20473078).
N-甲硝胺异构化和分解反应机理和动力学的理论研究
韦文美 ,郑仁慧 ,田燕 ,何天敬* ,何力 ,陈东明 ,刘凡镇
摘要:
在QCISD(T)/6-311+G*//B3LYP/6-311+G*水平上详细地研究了N-甲硝胺(CH3NHNO2)异构化和分解反应的势能面, 探讨了其反应的可能机理. 计算结果表明, 四个最低能量的反应通道是:(i) N-NO2键断裂通道,(ii) CH3NHNO2先异构化为CH3NN(OH)O(IS2a), 然后IS2a异构化为其它异构体,(iii) HONO消除通道,(iv) CH3NHNO2先异构化为CH3NHONO(IS3), 然后IS3通过N-ONO或O-NO键断裂而分解. 用CTST理论计算了这些反应的最初反应步(决速步)的反应速率常数, 得到这些决速步在298-2000 K的阿仑尼乌斯公式为k6(T)=1014:8e-46:0=RT ,k7(T)=1013:7e-42:1=RT ,k8(T)=1013:6e-51:8=RT 和k9(T)=1015:6e-54:3=RT s-1. 在503-543 K时计算的总包反应速率常数和实验测得的速率常数吻合很好.通过分析这些反应的速率常数, 发现在低温下CH3NHNO2异构化为CH3NN(OH)O的反应是主要通道, 而在高温下N-NO2键断裂和CH3NHNO2异构化为CH3NHONO的通道与异构化为CH3NN(OH)O的反应通道竞争.
关键词:  N-甲硝胺,势能面,反应机理,过渡态理论, 反应速率常数
DOI:10.1360/cjcp2007.20(2).126.9
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