中文摘要：

为了研究外电场对氯甲烷分子光谱和解离特性的影响，采用密度泛函理论（density functional theory，DFT）B3LYP方法在6-311＋＋G（d，P）基组水平上研究了不同外电场（-0．03～0．03a．u．）对氯甲烷分子结构以及解离特性的影响，包括键长、分子能隙、红外光谱以及解离势能面等。计算结果表明，随着Z方向（C-Cl连线方向）外电场从-0，03a．u．逐渐增加到0，03a．u．，C-Cl键的键长逐渐增大而C-H键的键长几乎不变，分子能隙EG先增大后减小，当外加电场等于0．01a.u．时达到峰值。C-Cl伸缩（stretching，STR）振动的频率是逐渐减小的，而红外光谱（infrared，IR）振动强度是逐渐增加的。通过进一步计算研究发现，随着外电场（0～0，03a．U．）继续增强，CH3Cl分子的势能曲线逐渐降低，解离能逐渐减小。当外电场大约是0．04a．u．时解离能最小，发生解离。因此，可以通过改变外电场来控制CH3Cl分子的降解。

英文摘要：

In order to analyze the influence of external electric field on the molecular spectra and dissociation of methyl chloride, density functional （DFT） theory at B3LYP/6-311G＋＋（d,p） level is used to investigate the influence on the molecular structure of the chloromethane molecule and dissociation properties under different external electric field （-0.03～0.03 a.u.）, including molecular bond length, energy gap, IR spectra, dissociation curve and so on. The calculation results show that with external electric field increase from -0.03 a.u. to 0.03 a.u. step by step, on the Z direction（C-Cl line）, C-Cl bond length increases and C-H bond length is almost the same. When the external electric field is equal to 0.01 a.u., the peak value is reached. The molecular energy gap increases and then decreases. The C-Cl stretching （STR） vibration frequency gradually decreases, while infrared （IR） vibration intensity gradually increases. Further research and analysis indicate that with the continuous increase of the external electric field （0～0.03 a.u.）, the energy curve of CH3Cl molecule decreases gradually and the dissociation decreases too. When the external electric field is about 0.04 a.u., the dissociation energy is at the minimum, and the dissociation occurs. Therefore, it can control the degradation of the CH3Cl molecule by changing the external electric field.