【作者】 杨茂友；

【导师】 张庆刚； 杨传路；

【作者基本信息】 山东师范大学 ， 原子与分子物理， 2009， 博士

【摘要】 分子反应动力学是一门用分子层次的动力学行为来解释宏观化学反应的学科,它是化学动力学的一个重要分支。目前,人们已经能够对四原子体系进行准确的量子动力学计算研究。然而,化学和生物领域所涉及的反应包含有更多个原子,近年来6原子反应体系已经引起了较多科研工作者的兴趣。氯原子参与的化学反应在大气环境中占有非常重要的地位。在低温范围(200-300K)内,氯原子能够破坏大气层的臭氧层。在高温范围(1000-2500K)内它是典型的卤族元素和碳氢化合物的燃烧反应。而氯原子和甲烷的反应是卤素和有机物最简单的反应。这个反应能生成非常稳定的HCl分子,它是大气层中消除氯原子的一个重要渠道。所以近些年来,这一反应得到了广泛的研究,探索它的微观机理已经成为当前分子反应动力学的一个热门话题。在多原子分子反应动力学的研究中,由于体系涉及的独立坐标较多,使得构造其全维的势能面显得格外困难,同时量子动力学研究也需要约化维数的模型才能进行计算。本文是在较高水平的从头算基础上,采用修正的半经验势能函数,重新构建了Cl+CH4→HCl+CH3反应的全维势能面。并在新的势能面上,采用量子含时波包法和半刚性振转靶模型对本体系进行了详细的动力学计算研究,主要内容如下:(1)在Molpro2006程序包上,采用CCSD(T)/aug-cc-pvtz计算水平,优化了反应物、产物、鞍点和最小反应路径的几何结构和振动频率。依据这些从头算结果拟合了全维半经验势能函数中的所有参数。在拟合过程中不仅考虑了各稳定点的结构和频率而且也把实验反应速率常数数据作为标准进行了对比校正。然后讨论了新建势能面的一些特点。并采用经典的变分过渡态理论(CVT)和统一统计理论(CUS)对本反应的动力学进行了计算,与实验及其它理论结果的对比表明,当前新建的势能面能够精确地重现本反应体系的各种静态和动态性质。(2)在新建的势能面上,采用半刚性振转靶模型约化维数,对Cl+CH4→HCl+CH3反应进行了含时波包动力学计算。结果表明:第一,CH4基态反应几率随入射平动能的增加而平稳地上升,基态不存在明显的振动结构。第二,本体系反应几率总体上低于O+CH4,F+CH4等相似体系的反应几率,这说明Cl+CH4反应较难进行。第三,CH4的振动激发能显著地提高反应几率并且大幅降低反应阈能,同时CH4的第一、二振动激发态反应存在明显的振动结构。第四,不同的转动激发态也能明显地影响反应几率,但对反应阈能影响较小,且不同的空间立体构型对反应几率和反应阈能也都有影响。第五,给出了基态的总积分散射截面和反应速率常数,并和相应的实验以及其它理论结果进行了比较。(3)应用相似的方法,对同位素反应Cl+CD4→DCl+CD3进行了含时波包动力学计算,并对比研究了氘替代氢的同位素效应。研究表明:首先,同位素替代使得渐进态和过渡态的零点能发生了移动,造成了反应势垒的提高,加大了反应进行的难度。其次,同位素替代引起反应体系约化质量增加,进而造成了反应几率的降低。再次,对同位素替代前后不同振转激发态的反应几率分别进行了比较,发现存在明显的同位素效应。最后,给出了两同位素反应的散射截面和速率常数并和当前可以利用的实验及理论结果进行了比较。本文的创新点主要表现在以下方面:(1)提高了本体系依据的从头算数据的计算水平,纠正了以前势能面中发现的一些缺陷,构建了能够进行全局量子计算的全维势能面。(2)对本体系进行了含时波包动力学计算,给出了反应几率、总散射截面和速率常数等量子结果,当前计算所得结果能够与实验和其它理论数据较好的吻合,为进一步研究提供了理论数据,也为本体系的化学动力学研究作了有益的尝试。更多还原

【Abstract】 Molecular reaction dynamics, which uses the dynamics of molecular collision to understand the rules of macroscopic chemical reaction, is an important branch of chemical dynamics. At present, ones have been able to carry out the exact full-dimensional quantum dynamic calculation for the four-atomic system. But what chemistry and biology mostly concerns is the large reaction system containing more than four atoms. In resent years, the six-atomic reaction systems have attracted more researchers’attention.Chlorine atom chemistry is of great importance in the atmosphere over a wide temperature range. At low temperature (200-300K) range, Cl atom plays an active role as ozone destroyer. At high temperature (1000-2500K) range, it is important for halogen-hydrocarbon combustion. As a prototypical abio-organic reaction for combustion, the Cl+CH4→HCl+CH3 reaction has been widely studied in recent years. This is because that the reaction can eliminate chlorine atoms from the atmosphere by converting them into inactive HCl. So the reaction has been a hot topic in the molecular reaction dynamics at present.Firstly, in the theoretical dynamic study, the degrees of freedom are quite more for the atom-polyatomic reaction system, which make the ab initio calculations more difficult. Secondly, the quantum dynamic calculations still need reduced-dimensional model due to the limitation of the computer’ability at present. In this work, we developed a full-dimensional analytical potential energy surface (PES) for Cl+CH4→HCl+CH3 reaction, which took the formula of the semiempirical functions and was calibrated based on the new ab initio data at the CCSD(T)/aug-cc-pvtz level. Then, on this PES we carried out the time-dependent wave package dynamics study using semirigid vibrational rotation target model. The main content of this thesis can be summarized as follows:(1) Employing CCSD(T) method and aug-cc-pvtz basis sets in Molpro2006 program packages, we calculated the geometries and frequencies of saddle point, reactant and product for Cl+CH4 reaction. The reaction coordinate path was also optimized. Based on these ab initio data, a semiempirical PES was calibrated. In this process, the geometries and vibrational frequencies of the reactants, the products and the saddle point were adjusted, and the experimental rate constants are also emphasized. Then discussions were involved concerning some characters of the present PES. To test this PES, the reaction kinetic calculations were carried out by using canonical variational transition state theory and canonical unified statistical theory. The comparison with experiments exhibited the present PES could well display both static and dynamical properties of the Cl+CH4→HCl+CH3 reaction(2) A four dimensional quantum dynamics study was reported on the new developed potential energy surface for Cl+CH4→HCl+CH3 reaction. We employed time-dependent wave package method to propagate wave function and semirigid vibrational rotation target model to reduce the system dimensions. Initial state-specific reaction probabilities were calculated and compared with the results of hydrogen absorption reactions O+CH4 and F+CH4. The ground state rate constants were given and in agreement with the experimental measures. The effects of reactant rovibrational excitation were investigated. Sterically dynamical effects of the reactants were also revealed.(3) By using the same method, a time-dependent wave packet dynamic study for the isotope effects of the Cl+CH4/CD4 reactions was conducted. The initial state-specific probabilities exhibited the replacement of hydrogen by deuterium significantly decreased the reaction ability, and the rovibrational excitations of the methane molecule favored the progress of the reaction. Additionally, the ground state rate constants were reported.The important and valuable results in this dissertation can be summarized as follows:(1) The ab initio calculation level of the reaction system was improved and some defects existed in the previous potential energy surface of the system were corrected. A modified global PES was constructed.(2) On the system, the time-dependent quantum dynamic calculations were conducted and provide the reasonable results including the reaction probability, the total scattering cross section and the rate constant, which were in well agreement with the related experimental data. This work has carried out a beneficial trial for the theoretical and experimental research of the Cl+CH4→HCl+CH3 reaction.更多还原