Absorption and magnetic circular dichroism (MCD) spectroscopies are powerful and simple methods to discriminate among various compounds. Polycyclic aromatic hydrocarbons provide particularly strong signal, which, for example, facilitates their detection in the environment. However, interpretation of the spectra is often based on quantum-chemical simulations, providing a limited precision only. In the present work, we use time-dependent density functional theory and complete active space second-order perturbation theories to understand spectral features observed in a series of naphthalene, anthracene, phenanthrene, and three larger compounds. The electronic computations provided reasonable agreement with the experiment for the smaller molecules, while a large error persisted for the bigger ones. However, many discrepancies could be explained by vibrational splitting of the electronic transitions across the entire spectral range. Compared to plain absorption, MCD spectral bands and their vibrational splitting were more specific for each aromatic molecule. The computational tools allowing simulations of detailed vibrational features in the electronic spectra thus promise to open a qualitatively new chapter in the spectroscopy of aromatic compounds.

中文翻译：

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多环芳烃的电磁圆二色性光谱中的振动结构

吸收光谱和磁性圆二色性（MCD）光谱学是区分各种化合物的强大而简单的方法。多环芳烃提供特别强的信号，例如，这有助于在环境中对其进行检测。但是，光谱的解释通常基于量子化学模拟，仅提供有限的精度。在当前的工作中，我们使用时变密度泛函理论和完整的活性空间二阶扰动理论来理解在一系列萘，蒽，菲和三种较大化合物中观察到的光谱特征。电子计算为较小的分子提供了与实验的合理一致性，而较大的分子则仍然存在较大的误差。然而，许多差异可以通过整个光谱范围内电子跃迁的振动分裂来解释。与普通吸收相比，MCD谱带及其振动分裂对每个芳族分子更具特异性。因此，允许对电子光谱中的详细振动特征进行仿真的计算工具有望为芳香族化合物的光谱学打开新的篇章。