外电场下二氧化硫的分子结构及其特性

Molecular structure and properties of sulfur dioxide under the external electric field

以6-311++g(3d,p)为基组,采用B3P86方法研究了不同外电场(-0.04—0.04 a.u.)对SO_2分子基态的几何参数、电荷分布、能量、电偶极距、最高占据轨道(HOMO)能级、最低占据轨道(LUMO)能级及能隙的影响,在优化构型的基础上,采用含时密度泛函(TD-B3P86)方法研究了SO_2分子在外电场作用下前9个激发态的激发能、跃迁波长和振子强度.研究表明:SO_2的几何参数与电场强度大小及方向均有明显的依赖关系.电场由-0.04 a.u.变化至0.04 a.u.时,体系的总能量先增加后减小;偶极矩先减小后增加;HOMO能级一直减小;LUMO能级先增加后减小;能隙先增加后减小.激发态的激发能、跃迁波长和振子强度与电场关联均较为复杂,说明SO_2的激发特性易受外电场影响.

SO2 is not only an important resource but also a notorious air pollutant, so it has attracted increasing attention nowadays. This paper focuses on the influence of external electric field on SO2. In order to obtain more reliable results,the density functional theory B3P86 method is chosen to calculate the values mentioned below. The ground states of SO2 molecule under different strong electric fields ranging from-0.04 a.u. to 0.04 a.u. are optimized by density functional theory B3P86 method with 6-311＋＋g（3d, p） basis sets. The geometric parameters, charge distributions, total energies, dipole moments, the highest occupied molecular orbital（HOMO） energies, the lowest unoccupied molecular orbital（LUMO） energies, energy gaps of SO2 under different external electric fields are obtained, respectively. On the basis of optimized configuration, the excitation energy, transition wavelength and oscillator strength in the same intense external electric field are calculated by the time dependent density functional theory（TD-B3P86） method.The calculated values for geometric parameters of SO2 without external electric field agree well with the available experimental data and other theoretical results. The geometric parameters and charge distribution of SO2 strongly depend on the intensity and direction of external electric field. The total energy of SO2 in the considered range of external electric field first increases and then decreases. On the contrary, the dipole moments of SO2 in different external electric fields ranging from -0.04 a.u. to 0.04 a.u. first decrease and then increase. When the external electric field is-0.04 a.u., the total energy and symmetry of SO2 both reach the maximum values. With the change of external electric field, the LUMO energy first increases and then decreases. The HOMO energy is found to decrease through the variation of the external field. The energy gaps of SO2 are proved to first increase, and then decrease with the variation of external electric field. Through studying the energy gaps of SO2, it is found that the external electric field can affect the chemical reactivity of SO2. The excitation energies, transition wavelengths and oscillator strengths are very complicated with the change of the external electric field. The excitation properties of SO2 molecule are seriously affected by the external electric field.