Department of Chemistry and Ames Laboratory, Iowa State University, Ames, Iowa 50011, United States.
J Phys Chem A. 2011 May 12;115(18):4574-82. doi: 10.1021/jp112230f. Epub 2011 Apr 14.
Highly accurate excitation spectra are predicted for the low-lying n-π* and π-π* states of uracil for both the gas phase and in water employing the complete active space self-consistent field (CASSCF) and multiconfigurational quasidegenerate perturbation theory (MCQDPT) methods. Implementation of the effective fragment potential (EFP) solvent method with CASSCF and MCQDPT enables the prediction of highly accurate solvated spectra, along with a direct interpretation of solvent shifts in terms of intermolecular interactions between solvent and solute. Solvent shifts of the n-π* and π-π* excited states arise mainly from a change in the electrostatic interaction between solvent and solute upon photoexcitation. Polarization (induction) interactions contribute about 0.1 eV to the solvent-shifted excitation. The blue shift of the n-π* state is found to be 0.43 eV and the red shift of the π-π* state is found to be -0.26 eV. Furthermore, the spectra show that in solution the π-π* state is 0.4 eV lower in energy than the n-π* state.
采用完全活性空间自洽场（CASSCF）和多组态准简并微扰理论（MCQDPT）方法，预测了尿嘧啶低能 n-π* 和 π-π* 态的激发光谱，在气相中和水中均具有很高的精度。通过 CASSCF 和 MCQDPT 实现有效片段势能（EFP）溶剂方法，可以预测高度精确的溶剂化光谱，并直接根据溶剂与溶质之间的分子间相互作用来解释溶剂位移。n-π* 和 π-π* 激发态的溶剂位移主要源于光激发后溶剂与溶质之间静电相互作用的变化。极化（诱导）相互作用对溶剂位移激发的贡献约为 0.1 eV。发现 n-π* 态的蓝移为 0.43 eV，π-π* 态的红移为-0.26 eV。此外，光谱表明在溶液中，π-π* 态的能量比 n-π* 态低 0.4 eV。
