间二甲苯分子在不同外电场下结构和解离特性研究

间二甲苯是挥发性有机物(VOCs, Volatile Organic Compounds)的关键活性成分,研究其在外电场下的性质十分重要.采用密度泛函理论(DFT),在B3LYP/6-311G++基组水平上对间二甲苯分子进行优化,从分子结构研究了不同外电场(-0.025 a.u.～0.025 a.u.)作用下,间二甲苯分子的总能量,键长,电偶极矩,前线轨道,红外光谱和解离势能面.计算结果表明,沿两甲基中C原子连线方向的电场(-0.025 a.u.～0.025 a.u.)增加时,分子总能量和能隙先增大后减小,电偶极矩先减小后增加.通过计算发现外电场对间二甲苯分子不同键长和不同振动模式的红外光谱的影响均有所不同.间二甲苯分子的解离特性表现为:沿两甲基中C原子连线方向施加强度超过0.047 a. u.的电场时,位于电场增加方向的甲基与苯环之间起连接作用的C-C键断裂.以上计算结果可为利用电场降解间二甲苯提供重要理论参考.

Study on structure and dissociation properties of m-xylene under external electrical fields

M-xylene is the key ingredient of volatile organic compounds (VOCs), so it is necessary to study the properties of m-xylene under external electrical fields. In this paper, the density functional theory at the B3LYP/ 6-311G++ level is employed to study the total energies, bond lengths, dipole moments, frontier orbital energies, infrared spectrum and dissociation potential energy surfaces of m-xylene under different external electrical fields. The obtained results show that, with gradually increasing the external field(-0.025 a.u. ~ 0.025 a.u.) along the ligature of two carbon atoms of the two methyl groups, the total energies and energy gap of m-xylene increase initially and then decrease, while the dipole moment decreases initially and then increases. In the study, we also found that the variations of diverse bond lengths and infrared vibration under different external electric fields are different. Further studies show that with increasing the external electric field (0 ~ 0.047 a.u.) along the ligature of two carbon atoms of the two methyl groups, the dissociation potential energy surface along C-C bond that is between benzene ring and methyl in the direction of the increase of the electric field becomes unbound with disappearing of potential barrier. The results can provide an important reference for the degradation of m-xylene via the external electric field.