Core hole effect in NEXAFS spectroscopy of polycyclic aromatic hydrocarbons: Benzene, chrysene, perylene, and coronene
Core hole effect in NEXAFS spectroscopy of polycyclic aromatic hydrocarbons: Benzene, chrysene, perylene, and coronene
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DOI：
10.1063/1.477696
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发表时间：
1998-12-15
影响因子：
4.4
通讯作者：
Kosugi, N
中科院分区：
文献类型：
--
作者：
Oji, H;Mitsumoto, R;Kosugi, N
利用同步辐射测量了金、苝和晕苯的碳K边NEXAFS谱，并对测量结果进行了从头算分析。该谱与计算的未占态密度（DOUS）不一致，表明显着的芯-空穴效应导致NEXAFS谱偏离DOUS。另一方面，通过改进的虚轨道方法，考虑到这种影响，理论计算很好地模拟了观测光谱。这使得详细分析的核心空穴效应，影响过渡能量和强度。在分析过程中，还对苯中的核孔效应进行了分析。结果表明，芯-空穴效应的大小与激发位和末态空轨道的组合密切相关。这种依赖性可以半定量地解释的激发位点和最终状态的轨道模式的组合。NEXAFS谱与DOUS谱的严重偏离主要归因于芯-空穴效应的这种变化，另外还有与位置相关的芯电离能的影响。在某些情况下，即使是跃迁到相同的空轨道也会导致不同的光谱特征，或者一个明显的单一光谱特征由跃迁到不同的空轨道组成。因此，直接的信息DOUS的分子与这样的不等价的网站是无法获得的NEXAFS光谱，虽然较小的偏差，建议为其他系统与单一的网站，如C-60和石墨中的C原子，和N原子的锌四苯基卟啉。(C)1998年美国物理学会。[S0021-9606（98）00147-0]。
Carbon K-edge NEXAFS spectra of chrysene, perylene, and coronene were measured using synchrotron radiation, and the results were analyzed by ab initio molecular orbital (MO) calculations. The spectra do not agree well with the calculated density of unoccupied states (DOUS), indicating significant core-hole effect leading to deviation of the NEXAFS spectra from the DOUS. On the other hand, the observed spectra were well simulated by theoretical calculations taking this effect into account by the improved virtual orbital method. This allowed a detailed analysis of the core-hole effect, which affects both transition energy and intensity. During the course of this analysis, the core-hole effect in benzene was also analyzed. It was found that the magnitude of the core-hole effect is strongly dependent on the combination of the excited site and final vacant orbital. This dependence could be semiquantitatively explained in terms of the combination of the excitation site and the orbital patterns of the final state. The severe deviation of the NEXAFS spectra from the DOUS is ascribed mainly to such variation of the core-hole effect, with additional effect by the site-dependent core ionization energy. In some cases, even the transitions to the same vacant orbital contribute to different spectral features, or an apparently single spectral feature consists of transitions to different vacant orbitals. Thus direct information about DOUS of a molecule with such inequivalent sites is not obtainable from the NEXAFS spectrum, although smaller deviation is suggested for other systems with single site, such as the C atoms in C-60 and graphite, and the N atoms in Zn tetraphenyl porphyrin. (C) 1998 American Institute of Physics. [S0021-9606(98)00147-0].