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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Model Hamiltonian Approach to the Infrared Intensities of Charged Conjugated π-Electron Systems
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Model Hamiltonian Approach to the Infrared Intensities of Charged Conjugated π-Electron Systems

机译：带电共轭π-电子系统红外强度的模型哈密顿方法

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摘要

The changes in electronic structures generating large dipole derivatives for the CC stretches in charged conjugated (π-electron) hydrocarbon species are analyzed theoretically by deriving a relation between dipole derivatives and electric-field-induced changes in bond orders and by constructing a simple model Hamiltonian. The model Hamiltonian consists of the diagonal term representing the electric-field dependence of the energy on each site (carbon atom) and the off-diagonal term taken from the Su-Schrieffer-Heeger model. It is shown that the dipole derivatives calculated with the model Hamiltonian are in reasonable agreement with those obtained at the B3LYP/6-311G~* level of density functional theory. It is concluded that the model Hamiltonian adequately describes the mechanisms that determine the signs and magnitudes of the dipole derivatives of the CC stretches in charged conjugated hydrocarbon species. For neutral species, the dipole derivatives of all the CC stretches are calculated to be zero by the model Hamiltonian. This is a consequence of the pairing theorem that holds for the molecular orbitals of the model Hamiltonian for alternant hydrocarbons and is consistent with the experimental results that the IR intensities are weak in the fingerprint region for neutral species. As examples of the application of the present approach, detailed analyses of the changes in the electronic structures generating dipole derivatives of the CC stretches are carried out for the radical cations of naphthalene, pentacene, biphenyl, perylene, and biphenylene, as well as for some related species.
机译：通过推导偶极导数与电场诱导键序变化之间的关系并构建简单的模型哈密顿量，从理论上分析了为带电共轭（π电子）烃类化合物的CC拉伸生成大偶极导数的电子结构变化。哈密​​顿量模型由代表能量在每个位点（碳原子）上的电场依赖性的对角项和取自Su-Schrieffer-Heeger模型的非对角项组成。结果表明，用哈密顿量模型计算出的偶极导数与在密度泛函理论的B3LYP / 6-311G〜*水平获得的偶极导数基本吻合。结论是，模型哈密顿量充分描述了确定带电共轭碳氢化合物中CC链段偶极导数的符号和大小的机制。对于中性物种，哈密顿量模型将所有CC延伸的偶极导数计算为零。这是配对定理的结果，配对定理适用于交替碳氢化合物的哈密顿量模型的分子轨道，并且与实验结果一致，即中性物种的指纹区中红外强度很弱。作为本方法的应用实例，对萘，并五苯，联苯，per和联苯的自由基阳离子，以及某些化合物的CC伸展产生偶极导数的电子结构的变化进行了详细分析。相关物种。

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