高精度量子化学计算方法研究甲酸甲酯的分解反应 毕业论文.doc

高精度量子化学计算方法研究甲酸甲酯的分解反应 总计： 毕业论文 18 页 表格 8 表 插图 3 幅 指导教师： 评阅人： 完成日期： 摘 要 一氧化碳是工业合成上常用的一碳源，然而由于它的毒性以及生产、运输过程中操作的复杂性，它的使用受到了一定程度的限制。近年来，化学家们开始寻找新的一碳来源。甲酸甲酯作为一种一氧化碳液体来源受到了广泛的关注。 本文采用量子化学从头算方法研究了甲酸甲酯分解反应的两个不同反应路径：分解成CO与CH3OH（反应1）和分解成CO2与CH4（反应2）。在不同的方法、基组下，分别考察了两个反应的活化能、Gibbs自由能和反应焓变情况，并与已有实验结果进行了比较。 研究结果表明：1）甲酸甲酯分解为一氧化碳的反应（1）为简单基元反应，只经历了一个过渡态；而反应（2）是一个两步反应，经历了两个过渡态。2）各种计算水平所得到的稳定点及过渡态的几何结构差异不大，并与已有实验结果较好地相符合，然而，能量计算值的差异较大，说明相关能效应影响是重要的。3）高精度的G2计算数值与实验值符合较好。在温度400K、500K下，对于两个分解反应，Gibbs自由能的计算误差与实验值相比均小于2kcal/mol，处于计算化学精度之内。特别地，在298.15K下，利用G2方法得到的计算反应焓变分别 45.76kJ/mol（反应1）和-111.79kJ/mol（反应2），与实验值相差仅为1.79kJ/mol（反应1）和0.71kJ/mol（反应2）。 关键词：甲酸甲酯 高精度从头算方法 过渡态 反应势垒 ABSTRACT As a C1 gas source, carbon monoxide is used widely in industrial synthesis. However, there are many limits to the use of carbon monoxide due to its hard controlling, high toxicity and easy to explosion in storage and transportation. Therefore, for decades, chemists have tried to find a new C1 source as a substitute of CO. Recently, methyl formate as a liquid C1 source came into our eyes. In this paper, quantum chemistry ab initio methods are employed to study the dissociation of methyl formate in two ways:1) CO and CH3OH (reaction 1) and 2) CO2 and CH4 (reaction 2). The active barriers, Gibbs free energies and reaction enthalpies at various levels are calculated and compared with available experimental results. The results suggest that 1) reaction 1 is a simple element reaction, in which one transition state is found; while reaction 2 is a two-step reaction, in which two transition states are found. 2) the geometries of the reactants, products and transition states for both reactions are similar at various calculation levels, and in consistent with available experimental values. However, the differences of calculation energies are large relatively, which implies that the correlation energy is very important. 3) High accuracy G2 calculations are in good agreement with experim