多电荷萘及其C10H8异构体：成键、光谱和在AGN环境中的应用
Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy and implications in AGN environments
摘要：
萘（C10 H8）是最简单的多环芳烃（PAH），是一系列涉及烃类的天体化学反应的重要组分。它的分子电荷状态影响其异构结构的稳定性，这在电离的天体物理环境中特别相关。因此，我们进行了广泛的计算搜索的低能量分子结构的中性，单，多电荷萘及其异构体的电荷状态+q = 0-4，并调查其几何性质和成键的情况。我们发现，异构化反应应该是频繁的更高的电荷状态和开链占主导地位的低能量结构。我们计算选定的低能量物种的标度谐波和非谐波红外光谱，并提供计算的比例因子为萘中性，阳离子和双阳离子的全球最小值。所有的模拟光谱再现令人满意的实验数据，因此，是足够的辅助观测。此外，利用萘光解截面σ ph-d的实验值，在一组相关的源中，确定了在高能X射线光子通量下，这些物种在活动星系核（AGN）环核区发射光谱中的潜在存在，并确定了其在光子能量为2.5 keV时的半衰期t_{1/2}。最后，我们表明，计算的三重和四重电荷的物质的红外波段能够再现选定的活动星系核源的一些功能。
英文摘要：
Naphthalene (C10H8) is the simplest polycyclic aromatic hydrocarbon (PAH) and an important component in a series of astrochemical reactions involving hydrocarbons. Its molecular charge state affects the stability of its isomeric structures, which is specially relevant in ionised astrophysical environments. We thus perform an extensive computational search for low-energy molecular structures of neutral, singly, and multiply charged naphthalene and its isomers with charge states +q = 0-4 and investigate their geometric properties and bonding situations. We find that isomerisation reactions should be frequent for higher charged states and that open chains dominate their low-energy structures. We compute both the scaled-harmonic and anharmonic infrared spectra of selected low-energy species and provide the calculated scaling factors for the naphthalene neutral, cation, and dication global minima. All simulated spectra reproduce satisfactorily the experimental data and, thus, are adequate for aiding observations. Moreover, the potential presence of these species in the emission spectra of the circumnuclear regions of active galactic nuclei (AGNs), with high energetic X-ray photon fluxes, is explored using the experimental value of the naphthalene photodissociation cross-section, σ_{ph-d}, to determine its half-life, t_{1/2}, at a photon energy of 2.5 keV in a set of relevant sources. Finally, we show that the computed IR bands of the triply and quadruply charged species are able to reproduce some features of the selected AGN sources.
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