Dissertation > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Structural Chemistry > Chemical bond theory

Theoretical Study of Activation C-H Bond of Methane by Ti, Zr, Hf in the Gas Phase

Author CuiDanDan
Tutor WangYongCheng
School Northwest Normal University
Course Physical and chemical
Keywords Ti Zr Hf Density functional theory (DFT) Minimum energy crossing point (MECP) Spin - orbit coupling (SOC)
CLC O641.1
Type Master's thesis
Year 2010
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In recent years, the transition metal M and its oxides MO , cationic and small organic molecules in the gas phase catalytic reaction and found that the transition metals and their oxides cations on the CH bond of small organic molecules in the study, CO has a unique key and CC bond activation. Also found that the reaction of people in the process of studying this type of reaction in the ground state of the reactants and the product of the ground state usually has a different spin states, appear frequently before and after the spin multiplicity change phenomenon throughout the thermal reaction, that reaction does not comply with the \. \The potential energy surface of the reaction process involving two or more, and the reaction is always maintained at a low energy of the potential energy surface, such reactions are usually referred to as \However, due to the limitation and the impact of the spin conservation law for the prevailing experimental conditions, this flip Because spin caused by reactants and products have a different spin states phenomenon often overlooked in the reaction. Until 1994, with the development of high-tech experimental means, during the reaction people monitored the class reaction indeed contrary to the spin conservation law, the potential energy surface cross argument was only the two-state reaction of the fundamental mechanisms slowly accepted. To better explain these phenomena, inspire more in-depth study of the two-state reaction, and the two-state reaction TSR is still the focus of attention of chemistry enthusiasts around the world. According to the principle of the two-state reactivity (TSR), the use of density functional theory for transition metal activation of small molecules spin-forbidden reaction depth computing research. Optimize the reaction potential energy surfaces of different spin states with a high level of basis set, using the method of Harvey optimize different potential energy surface cross sewn on the minimum energy crossing point (MECP) calculated MECP at spin - orbit coupling matrix elements using group theory irreducible representations of the direct product of the theoretical analysis of the reaction system is the vibration on the spin - orbit coupling. Reference Andrews et al experimental observations, Ti, Zr, Hf transition metal activated CH 4 Reaction Mechanism of CH bond depth theoretical study. The text is divided into four chapters. The first chapter gives an overview of the theoretical basis of quantum chemical ab initio methods, applications, and the two-state reaction theory of progress and research status. The second chapter briefly describes the basic theory, including the selection rules of spin - orbit coupling mechanism and the Department of intersystem crossing. The first two chapters are mainly summarizes the theoretical background and theoretical basis of this work, our study provides a reliable quantum chemical methods. The third chapter, Chapter IV, we use the density functional theory and advanced electronics coupled cluster method in CCSD/6-311 G (3df, 3pd) / / UB3LYP/6-311 G (3df, 3pd) the theoretical level studied under three spin states of Ti, Zr, Hf atoms in the CH bond activation in CH 4 molecules one by one to win the microscopic reaction mechanism of H atoms. First, the use of high-precision calculation of basis sets optimized geometries of different spin potential energy surface of the stationary points of the different reaction path. Second, the reaction path to do a simple description of the microscopic mechanism of the reaction at a glance. Third, first with Hammond assumptions to deduce the approximate location of the potential energy surface crossing, further use of the the Yoshizawa intrinsic vertical coordinate single point excited state cross-point (CP) method to determine the potential energy surface structure and relative energy, and finally discuss its for The reaction efficiency and the reaction rate of the overall reaction. Fourth, the use of methods of mathematical algorithms Harvery people find the reaction hypersurface of minimum energy crossing point (MECP), and then in two different electronic potential energy surface of the cross seam, and discuss its impact for the overall reaction efficiency . Fifth, we chose this crossing point for representatives to discuss the behavior of spin flip, the study of a potential energy surface cross the point spin - orbit coupling (SOC) to analyze the \good reaction channel. The results show that the above reaction is a typical two-state reaction, singlet and triplet two potential energy surfaces during the reaction cross crossover occurs before the transition state, it is largely affected the efficiency of the reaction and the reaction rate, calculated spin - orbit coupling constant is very small, so that the non-adiabatic reaction probability of small intersystem crossing between two potential energy surfaces.

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