Excited State ab Initio and Franck鈥揅ondon Simulation of S1 鈫?i> S0 Fluorescence Excitation Spectra of p-, m-, and o-Difluorobenzenes

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• 作者：Qianliu Yang ; Rongxing He ; Wei Shen ; Huabing Li ; Ming Li ; Chaoyuan Zhu ; Sheng Hsien Lin
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：December 8, 2011
• 年：2011
• 卷：115
• 期：48
• 页码：14022-14033
• 全文大小：954K
• 年卷期：v.115,no.48(December 8, 2011)
• ISSN：1520-5215

文摘

Although difluorobenzenes (DFBs) are well-known organic molecules to understand the electronic structure and spectroscopy of benzene and its derivatives, few theoretical investigations have been performed to simulate their fine spectra and assign their vibrational bands. In this work, the fluorescence excitation (FEX) spectra of the first excited singlet states for three DFBs molecules (para-, meta- and ortho-difluorobenzene) were simulated by the Franck鈥揅ondon calculations with the displaced harmonic oscillator approximation plus the distorted correction. The calculated results indicated that the spectral profiles of three DFBs are primarily described by the Franck鈥揅ondon progression of their totally symmetric vibrational modes. Specifically, it is found that modes v₃ and v₅ of para-DFB, v₈ and v₉ of meta-DFB, and ortho-DFB play the most important roles in the fluorescence spectra. By taking into account the contributions of the distorted effect, we could assign most of the dominant overtones from the nontotally symmetric vibrational modes, and the results agree well with the experimental assignments. Some inferred and unassigned vibrational transitions in experiment were confirmed according to the present calculated results. In addition, in the simulated fluorescence spectra, we tentatively assigned several combination bands with relative moderate intensity and weak vibrational lines which appeared in the experimental observations but the corresponding assignments were not given. The present work reproduced satisfactorily the experimental FEX spectra of p-, m-, and o-DFBs derivatives and provided a useful method to simulate the FEX spectra of dihalogenated benzene molecules.