A combined theoretical and experimental study of the valence and Rydberg states of iodopentafluorobenzene
A combined theoretical and experimental study of the valence and Rydberg states of iodopentafluorobenzene
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DOI：
10.1063/1.4981919
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发表时间：
2017-05-07
影响因子：
4.4
通讯作者：
Biczysko, Malgorzata
中科院分区：
文献类型：
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作者：
Palmer, Michael H.;Hoffmann, Soren Vronning;Biczysko, Malgorzata
报道了用同步辐射对五氟碘苯(C6F5I)进行紫外(UV)和真空紫外光(VUV)光谱的研究。这些测量结果与最近一项高分辨率光电子能谱研究的结果相结合。一项重要的理论研究，包括Franck-Condon(FC)和Herzberg-Teller(HT)分析，得出了与这两个实验研究相一致的结论。我们观察到VUV光谱中7.926 eV的VUV多重态是里德堡态而不是价态，这导致了与以前的研究相比，VUV里德堡谱发生了根本的重新分配，并消除了一个反常现象，即一些先前分配的里德伯格态被指定为光学禁止态。绝热激发能(AEEs)由单激发和双激发耦合的团簇运动方程确定，并与含时密度泛函方法相结合。这两种方法的频率非常相似，这使得能够在较低的价态下评估FC和HT的贡献。多参考多根组态相互作用令人满意地解释了C6F5I的主要UV+VUV谱，以及垂直带位置和强度。紫外光谱由两个非常弱的跃迁组成，分别对应于1(1)B(1)(pi sigma*)和1(1)B(2)(sigma sigma*)对称性。Sigma*(a(1))对称性的最低空位分子轨道具有显著的C-I*反键特征。这导致这两个激发态的C-I键显著延长。最低的11B1态的振动强度主要由HT贡献主导；1(1)B(2)态同时包含HT和FC贡献；第三带包含三个态，两个pi Pi*(1(1)A(1)，2(1)B(2))和一个pi sigma*(2(1)B(1))，在(1)A(1)态中由FC贡献主导。在这个(1)A(1)态，光谱优势带在6.7((1)A(1))和7.3 eV((1)A(1)+B-1(2))附近，C-I键长在正常范围内，FC组分占主导地位。由AIP出版公司出版。
A new ultraviolet (UV) and vacuum ultraviolet (VUV) spectrum for iodopentafluorobenzene (C6F5I) using synchrotron radiation is reported. The measurements have been combined with those from a recent high-resolution photoelectron spectroscopic study. A major theoretical study, which includes both Franck-Condon (FC) and Herzberg-Teller (HT) analyses, leads to conclusions, which are compatible with both experimental studies. Our observation that the VUV multiplet at 7.926 eV in the VUV spectrum is a Rydberg state rather than a valence state leads to a fundamental reassignment of the VUV Rydberg spectrum over previous studies and removes an anomaly where some previously assigned Rydberg states were to optically forbidden states. Adiabatic excitation energies (AEEs) were determined from equations-of-motion coupled cluster with singles and doubles excitation; these were combined with time dependent density functional theoretical methods. Frequencies from these two methods are very similar, and this enabled the evaluation of both FC and HT contributions in the lower valence states. Multi-reference multi-root configuration interaction gave a satisfactory account of the principal UV+ VUV spectral profile of C6F5I, with vertical band positions and intensities. The UV spectral onset consists of two very weak transitions assigned to 1(1)B(1) (pi sigma*) and 1(1)B(2) (sigma sigma*) symmetries. The lowest unoccupied molecular orbital of a sigma*(a(1)) symmetry has a significant C-I* antibonding character. This results in considerable lengthening of the C-I bond for both these excited states. The vibrational intensity of the lowest 11B1 state is dominated by HT contributions; the 1(1)B(2) state contains both HT and FC contributions; the third band, which contains three states, two pi pi*(1(1)A(1), 2(1)B(2)) and one pi sigma*(2(1)B(1)), is dominated by FC contributions in the (1)A(1) state. In this (1)A(1) state, and the spectrally dominant bands near 6.7 ((1)A(1)) and 7.3 eV ((1)A(1) + B-1(2)), the C-I bond length is in the normal range, and FC components dominate. Published by AIP Publishing.