二溴甲烷分子在外电场下物理性质及逐步解离特性研究

二溴甲烷在太阳光辐射下分解成破坏臭氧的溴自由基，严重危害自然环境和人类健康，研究对二溴甲烷的降解很有必要.利用密度泛函理论在B3LYP/6-311G(d, p)基组水平上研究了不同外电场(0～0.025a.u.)作用下二溴甲烷分子的物理性质，包括总能量、键长、电偶极矩、能级、能隙、红外光谱等.采用含时密度泛函理论在同样基组水平下研究了外电场对分子激发态的影响.此外，外电场下扫描两个C-Br键的势能曲线，发现外电场强度分别为0.025a.u.和0.04a.u.时两个C-Br键依次断裂分子发生逐步解离，该结果为保护环境即对二溴甲烷进行电场降解提供重要的参考依据.

Study on physical properties and stepwise dissociation characteristics of dibromomethane molecules under external electric field

Dibromomethane decomposes into ozone destroying bromine free radicals under sunlight radiation, which seriously endangers the natural environment and human health. It is necessary to study the degradation of Dibromomethane. The physical properties of Dibromomethane including total energy, bond length, electric dipole moment, energy level, energy gap, infrared spectrum under different external electric fields (0 ~ 0.025a. u.) are studied by using density functional theory at the B3LYP / 6-311G (D, P) basis set level. The effect of external electric field on molecular excited states is studied by using time-dependent density functional theory at the same basis set level. The potential energy curves of two C-Br bonds under external electric field are scanned separately, and it is found that when the external electric field intensities are 0.025a.u. and 0.04a.u., both the C-Br bonds are broken in turn and gradually dissociated. The results provide an important reference for the electric field degradation of Dibromomethane and hence for environmental protection.