外电场作用下苯乙烯分子结构和电子光谱

Molecular structure and electronic spectrum of styrene under the external electric field

采用密度泛函B3P86方法在6-311G基组水平上优化得到了在不同外电场(0—0.05 a.u.)作用下,苯乙烯分子的基态电子状态、几何结构、电偶极矩和分子总能量.在优化构型下利用杂化CIS-DFT方法(CIS-B3P86)研究了同样外电场条件下对苯乙烯的激发能和振子强度的影响.计算结果表明,分子几何构型与电场大小呈现强烈的依赖关系,分子偶极矩随电场的增加而增大.分子总能量随着电场增加而降低.激发能随电场增加快速减小,表明在电场作用下,分子易于激发和解离.

The ground states of styrene under different intense electric fields ranging from 0 to 0.05 a.u. are optimized using density functional theory DFT/B3P86 at 6-311G basis set level. The excitation energies and oscillator strengths under the applied electric fields are calculated employing the revised hybrid CIS-DFT method. The results show that the electronic state, molecular geometry, total energy, dipole moment, and excitation energy are strongly dependent on the applied electric field. As the electric field changes from 0 to 0.02 a. u., many of the bond lengths of C--H increase, while some of the bond lengths of C--H decrease. However, further increase of the electric field strength results in a increase of them both due to the charge transfer induced by the applied electric field. As to the bond lengths of C--C, some of them increase, some of them decrease and some of them remain unchanged as the electric field changes from 0 to 0.05 a. u.. The dipole moment of the ground state increases sharply with the applied field strength. With the electric field increasing, the total energy of the molecule decreases. The excitation energies of the first six excited states of styrene decrease with the increase of the applied electric field, indicating that the molecule is easy to be excited and dissociated under the electric field.