丙酮分子n→π跃迁光谱的平均溶剂静电势／分子动力学方法研究

Investigation of Spectrum Shift of N→π Transition for Acetone Molecule by Averaged Solvent Electrostatic Potential/Molecular Dynamics Method

采用量子力学/分子动力学方法研究了具体溶剂分子结构对溶质光谱行为的静电影响.通过拟合溶质所处外电场和引入溶剂分子极化率,考虑了溶质溶剂分子之间的相互极化效应,得到合理的溶质和溶剂分子的电荷分布.经过严格推导发现,在传统的显溶剂模型中,平衡和非平衡溶剂化能表达式均未考虑溶剂分子永久偶极弹簧能的贡献.因此,在正确计算永久偶极弹簧能的基础上,重新建立了溶剂化能的表达式和新的吸收/发射光谱移动公式.采用修改后的ASEP/MD程序,计算得到了与实验值比较吻合的丙酮在水溶液中n→π*跃迁的光谱移动值,验证了新公式的合理性.

Instead of continuous medium theory, quantum mechanics/molecular dynamics method was adopted to deal with the electrostatic effect on the spectrum of the solute molecule by considering the concrete structure of solvent molecules. By constructing the external electric field felt with solute molecule and introducing the molecular polarizability of the solvent molecule, the mutual polarization between the solute and the solvent was taken into account and reasonable charge distributions of the solute and the solvent molecule were obtained. With a detailed deduction, we found that the spring energy of the permanent dipole of the solvent molecule was ignored unreasonably in the expressions of the solvation energy for equilibrium and nonequilibrium states. Including the energy contribution of this part, the new expression for the solvation energy and formulas for the spectral shifts of light absorption and emission were established. With the modified averaged solvent electrostatic potential/molecular dynamics program, the calculated spectral shift of the N→π transition of acetone molecule in water is very close to the experimental value and the rationality of our new formula is testified.