氮原子簇的量子化学理论研究

2019-02-24 21:24:09

反应 结构 分解 31 原子簇









中文题名氮原子簇的量子化学理论研究

 





副题名 





外文题名 





论文作者王丽杰   





导师李前树教授   





学科专业应用化学   





研究领域\研究方向量子化学及其应用   





学位级别博士 





学位授予单位北京理工大学   





学位授予日期2001   





论文页码总数122页   





关键词量子化学  氮原子簇   





馆藏号BSLW

/2001

/O641

/95 





【中文摘要】

    摘 要
   对碳原子簇研究的热情激起了人们对氮原子簇研究的兴趣。由于氮原子簇的高能量性质而越来越受到人们的重视。本文选用了ab initio从头算和几种不同的DFT密度泛函理论方法,在6-31〓、6-311〓和6-311++〓基组下,对氮原子簇的结构、异构化反应途径、分解、合成机理和反应速率常数分别在热力学和动力学方面进行了量子化学计算研究,得到了一些创新性的结果,主要有:1. 在五氮原子簇中,优化和比较了四种〓的同分异构体,二种〓的同分异构体和一 种〓自由基。〓的能量最低,它们的能量依次为〓,其中预测了〓的盐合成机理和其结构 中6键迁移过程,即反应势能面。2.计算了八氮原子簇的五种开链结构〓和 〓,研究了四对〓异构体的异构化途径和〓中的6键迁移过程。由于开 链的〓有可能是环状或笼状结构分解过程中的中间体;因此,了解这些开链结构的 特性,对于我们进一步研究环状或笼状〓结构的分解机理具有一定的价值。我们又 研究了三个八氮原子簇的反应机理:〓(开链〓)→〓,〓和〓(五元环〓)反应。第一个的逆反应 为放热反应正反应为吸热反应,分解反应的能垒高度不够高(21.4kcal/mo1),因而〓 (〓)作为HEDM不够稳定,合成反应在很低的温度下即可发生。对于第二个反应, 其正反应为放热反应逆反应为吸热反应。在QCISD/6-311++〓∥B3LYP/6- 311++〓水平,分解反应的能垒高度为26.4kcal/mol,放热6.0kcal/mol。对 〓→Complex(〓)和〓→Complex(〓)反应,变分过渡态理论计算的速率 常数同校正的TST/W和TST/MEPSAG速率常数一致。〓和〓反应势能 面的研究为我们进一步理解八氮原子簇的分解和合成机理提供了理论依据。环状结 构的氮原子簇更稳定,作为HEDM,它是更有利的后选者;第三个反应是环状结构 〓的合成途径的设计。因此,本文所研究的势能面对于理解含更高能量的笼状 或环状结构的氮原子簇的分解或合成机理具有积极的意义。3. 我们得到了可能稳定的四种〓自由基的结构,四种〓的结构和一种〓。预测了它们 的几何结构、电子结构和谐振频率。最稳定的〓和〓的结构分别是〓,〓和〓。分析〓和〓的分解能和比冲;并在〓31G*T B3LYP/6-31G*水平下研究了〓和〓的分解过程,找到了它们的分解通道。在B3LYP/6-311+〓水平下的能垒高度为35.kcal/mol 〓〓 和15.4kcal/mol 〓和〓过程的能垒高度分别为2.1kcal/mol和4.3kcal/mol。从〓分解过程的能垒高度可知〓是亚稳态粒子,如果能被合成,则可用于HEDM。4.计算了十氮原子簇(原子和离子)的结构,优化了四种结构的〓的同分异构体;其中,〓对称性的一种〓的五种〓〓的三种〓。十氮原子簇的同分异构体在HF方法下优化,谐振频率均为正值。但在B3LY方法下部分结构的谐振频率计算出现虚频。〓的能量最低。其它几个稳定结构的能量依次为〓〓5.〓的同分异构体中〓对称性的结构只在HF/6-31G*下是稳定的;〓对称性的在HF/6-31G*和B3LYP/6-31G*下均是稳定的。〓和〓在HF/6-31G*和HF/D95*下均是个稳定点。但〓和〓在B3LYP/6-31G*下分解。〓〓和〓在HF/6-31G*下均是个稳定点;〓仅在HF/6-31G*水平下优化了几何结构,从能量上看,比〓对称性的〓稳定。总之,对氮原子簇结构和反应途径的研究,为其合成和应用奠定了坚实的理论基础。











【外文摘要】

 
ABSTRACT
The intense scientific and popular interest in 〓 molecule has naturally raised thequestion whether other important cluster species have been systematically overlooked. Arethere any other large stable molecules made of pure nitrogen? Nitrogen clusters have beenconsidered important for their higher energetic content. In this paper, the stability and structures of nitrogen clusters were investigated onkinetics and thermodynamics. The dissociated and synthesis PES of 〓and barrier height, tunneling effect were studied. The new characteristics of ourinvestigation on nitrogen clusters are formed by relating with the orders of nitrogen atomsforming clusters and studying the stability and structures on kinetics and thermodynamics. 〓 clusters have been optimized by ab initio and DFT methods with 6-31〓, 6-311〓and 6-311++〓basis sets. The structures, isomerization, decomposition and synthesispathway, reaction rate constant of nitrogen clusters have been studied on kinetics andthermodynamics. The main conclusions are as followed:1. The isomers of 〓and 〓 were studied, the order of their energies is 〓 < 〓 < 〓<〓<〓.The synthesis mechanism of 〓 and thePES of 6 -bond immigration were found.2. (a) The structures of 〓and 〓, four double 〓 isomersisomerization and 6 -bond immigration in 〓 were studied. (b) For the open-chainstructures may be the intermediates of cages and ring structures, therefore, the studies onthese structures are important. The pathways of 〓(open-chain, 〓) → 〓were studied. The barrier of the first reaction is 21.4kcal/mol and that of second reaction is 26.4 kcal/mol. The rate constants were also computed.(c) The potential energy surfaces for the synthesis and decomposition reactions of 〓 (five-membered, 〓 → 〓 were investigated by density functional theory (DFT). Thespecies involved were fully optimized using four DFT methods. Relative energies werefurther calculated at the QCISD/6-311+〓//B3LYP/6-311+〓level. The barrier heights of〓 →〓 + 〓 in forward and reverse directions were predicted to be 26.4 and 32.4kcal/mol, respectively. A calculation of rate constants for the dissociation and synthesispathway of 〓 was done by the VTST theory.3. The structures of 〓were optimized at HF/6-31〓, B3PW91/6-31 〓 and B3LYP/6-31 〓levels. The decomposition pathways of 〓and 〓were found on HF/6-31〓,B3PW91/6-31 〓 and B3LYP/6-31〓 PES. The barrier heights of the dissociation processes,in our best level, are 35.4 kcal/mol for 〓 →〓and 15.4 kcal/mol for〓→〓. Those of 〓 →〓and 〓→〓are 2.1 kcal/mol and 4.3 kcal/mol. From the barrier of the 〓 dissociation processes,we conclude that 〓is meta stable species and that it may be useful as a HEDM if it could besynthesized.4. The structures of 〓isomers 〓. They are all stationary points with HF method, but it isnot the same results with B3LYP method. The energy of 〓is the lowest pointamong these structures, the order on energies is: 〓.5. Geometries of 〓 isomers, 〓 and 〓 are calculated at HF/6-31〓, HF/〓and B3LYP/6-31〓 levels, respectively. The structure 〓 with 〓symmetry is stablestructure and could be a candidate of HEDMs. Another isomer, with 〓 symmetry, ispredicted to be unstable with nine imaginary frequencies at B3LYP/6-31〓 level although ithas no imaginary frequency with HF methods. 〓and 〓 are both localminima on HF/6-31〓and HF/〓 PES, but 〓and 〓dissociated onB3LYP/6-31〓 PES. 〓 with 〓symmetry is a local minimum on HF/6-31〓 PES.Geometric structures of 〓are determined to be stationary points at HF/6-31〓 level and characterized by all real frequencies. Geometric structure of 〓isoptimized at HF/6-31 〓 level.Therefore, the studies on the structures, the potential energies surfaces and the isomerizationreaction, would provide theoretical foundation for synthesizing more stable 〓 clusters asHEDMs in the future.