基于外电场作用对二溴苯的光谱特性和解离特性

Spectral and Dissociation Characteristics of p-Dibromobenzene Based on External Electric Field

对二溴苯(C6H4Br2)在化学工业领域有着广泛的应用,但也是威胁臭氧层的有机污染物之一,研究外电场作用下该分子的解离特性对臭氧层的保护具有重要参考价值。在不同外电场(-0.025~0.025 a.u.)作用下,采用密度泛函理论(density functional theory,DFT),B3LYP/6-311+G(d,p)基组水平上优化了对二溴苯分子的基态几何结构;采用含时密度泛函理论(time-dependent density functional method,TD-DFT)和B3LYP/6-311+G(d,p)基组计算了分子的紫外吸收光谱,推测分子的解离特性;对分子两个C—Br键的势能进行扫描,给出了对二溴苯分子解离特性的直接证据。研究表明,在外电场作用下,对二溴苯分子的基态几何结构、光谱特性、势能曲线及势能面均发生较大改变。随着外电场的增加,对二溴苯分子的3C—12Br键长、分子体系总能量均逐渐降低,6C—11Br键长、偶极矩逐渐增大;6C—11Br键长的增大,说明对二溴苯分子的6C—11Br键能减小,6C—11Br键更容易断裂。能隙随外电场增强先增大后减小,能隙的减小,说明分子更容易发生化学反应。C—Br键伸缩振动峰强度逐渐减小,紫外吸收光谱吸收峰强度先略微增大后猛然降低,红外光谱的振动频率和紫外吸收光谱的最强峰均发生了红移,表现出分子能量增强的特性,表明振动加强,化学键变得更活跃。在外电场作用下扫描了对二溴苯分子的3C—12Br键,得到了分子3C—12Br键的势能曲线,当外电场强度为-0.02 a.u.时,分子右侧势垒的最高能量与最低能量基本相平,分子3C—12Br键断裂;在此电场强度下继续扫描6C—11Br的势能发现,分子6C—11Br键也会断裂,因此对二溴苯分子可以发生逐步解离。在外电场作用下同时扫描对二溴苯分子的两个C—Br键,得到分子的势能面,当外电场强度为0.02 a.u.时,势能面的对角线势能降低,出现另一个解离通道,因此对二溴苯分子可能发生协同解离。上述结果为实验研究对二溴苯分子的外电场降解机理提供数据保障,也对该分子体系的解离特性研究有重要的参考意义。

P-dibromobenzene(C6H4Br2)has a wide range of applications in the chemical industry,but it is also one of the organic pollutants that threaten the ozone layer.The study of the dissociation characteristic of the molecule under an external electric field has important reference value for protecting the ozone layer.Under the action of different external electric fields(-0.025~0.025 a.u.),the p-dibromobenzene molecule is optimized based on B3LYP/6-311+G(d,p)based on density functional theory(DFT),the ground state geometric structure is computed.They are then using the Time-dependent density functional theory(TD-DFT)and B3LYP/6-311+G(d,p)basis set to calculate the ultraviolet absorption spectrum of the p-dibromobenzene molecule to guess the dissociation property of the molecule.Finally,scanning the potential energy of the two C—Br bonds of the molecule gave direct evidence of the dissociation property of the p-dibromobenzene molecule.Studies have shown that under the action of an external electric field,the ground state geometric structure,spectral characteristics,potential energy curve and potential energy surface of p-dibromobenzene molecules have undergone major changes.With the increase of the external electric field,the 3C—12Br bond length and total energy of the molecular system of p-dibromobenzene gradually decrease,and the 6C—11Br bond length and dipole moment gradually increase;the increase of the 6C—11Br bond length indicates that the 6C—11Br bond energy of p-dibromobenzene molecule is reduced,and the 6C—11Br bond is the easiest to break.The energy gap first increases and then decreases with the increase of the external electric field.The decrease in the energy gap indicates that the molecule is more prone to chemical reactions.The peak intensity at the stretching vibration of the C—Br bond gradually decreases.The peak intensity at the stretching vibration of the C—Br bond gradually decreased,and the absorption peak of the ultraviolet absorption spectrum increased slightly at first and then decreased abruptly.The energy-enhancing properties indicate that the vibrations intensify,and the chemical bonds become active.The 3C—12Br bond of the p-dibromobenzene molecule was scanned under an external electric field,and the potential energy curve of the 3C—12Br bond of the molecule was obtained.When the intensity of the external electric field is-0.02 a.u.,the highest energy of the right barrier of the molecule is the same as the lowest energy.Flat,the molecular 3C—12Br bond is broken;continue to scan the potential energy of 6C—11Br under this electric field strength,the molecular 6C—11Br bond is broken,so the p-dibromobenzene molecule will gradually decompose the separation phenomenon.Under the action of an external electric field,scan the two C-Br bonds of p-dibromobenzene simultaneously to obtain the molecule’s potential energy surface.When the external electric field intensity is 0.02 a.u.,the diagonal potential energy of the potential energy surface decreases,and another dissociation channel appears.Therefore,synergistic dissociation of p-dibromobenzene molecules may occur.These results provide data guarantee for the experimental study of the degradation mechanism of p-dibromobenzene molecules in an external electric field and have important reference significance for the study of the dissociation characteristics of the molecular system.