This article presents a comprehensive treatment of the polycyclic aromatic hydrocarbon (PAH) hypothesis. The interstellar, infrared spectral features which have been attributed to emission from highly vibrationally excited PAHs are discussed in detail. These include major (most intense) bands at 3040, 1615, "1310," 1150, and 885 cm-1 (3.29, 6.2 "7.7," 8.7, and 11.3 micrometers), minor bands and broad features in the 3200-2700 cm-1 [correction of 3200-2700-1] (3.1-3.7 micrometers), 1600-1100 cm-1 (6.0-9 micrometers) and 910-770 cm-1 (11-13 micrometers) regions, as well as the vibrational quasi-continuum spanning the entire mid-IR and the electronic transitions which contribute to the high-frequency IR continuum. All the major and minor bands, as well as the quasi-continuum, can be attributed to vibrational transitions in molecular-sized PAHs. The latter two broad features probably arise from very large PAHs, PAH clusters, and amorphous carbon particles. A precise match of the interstellar spectra with laboratory spectra is not yet possible because laboratory spectra are not available of PAHs in the forms probably present in the interstellar medium (completely isolated, ionized, some completely dehydrogenated, and containing between about 20 and 40 carbon atoms). The method with which one can calculate the IR fluorescence spectrum from a vibrationally excited molecule is also described in detail. Fluorescence band intensities, relaxation rates, and dependence on molecule size and energy content are treated explicitly. Analysis of the interstellar spectra indicates that the PAHs which dominate the infrared spectra contain between about 20 and 40 carbon atoms. The results obtained with this method are compared with the results obtained using a thermal approximation. It is shown that for high levels of vibrational excitation and emission from low-frequency modes, the two methods give similar results. However, at low levels of vibrational excitation and for the high-frequency modes (for example, the 3040 cm-1, 3.3 micrometers band), the thermal approach overestimates the emission intensities. For calculations of molecular reactions (such as H-loss, deuterium enrichment, and carbon skeleton rearrangement) a thermal approximation is invalid. The relationship between PAH molecules and amorphous carbon particles is presented and their production in circumstellar shells is described. The most likely interstellar PAH molecular structures are discussed and the possibility of destructive reactions with interstellar oxygen and hydrogen atoms is considered in detailed and found to be unimportant. Interstellar PAH size and abundance estimates are made. On the order of a few percent of the available interstellar carbon is tied up in the small (20-40 carbon atom) PAHs which are responsible for the sharp features, and a similar amount is tied up in the larger (200-500 carbon atom) PAHs or PAH clusters and amorphous carbon particles which are responsible for the broad components underlying the 1600-1100 and 900-770 cm-1 (6-9 and 11-13 micrometers) regions. It is shown that the spectroscopic structure these PAHs and PAH-related materials produce in the UV portion of the interstellar extinction curve lie just below current detection limits but fall in the range detectable by the Hubble Space Telescope. Finally, the influence of PAH charge on the ultraviolet, visible, and infrared regions is described.

中文翻译：

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星际多环芳烃：红外发射带，激发/发射机理和天体物理学意义。

本文介绍了对多环芳烃（PAH）假设的全面处理。详细讨论了星际，红外光谱特征，这些特征归因于高度振动激发的PAHs的发射。其中包括3040、1615，“ 1310”，1150和885 cm-1（3.29、6.2“ 7.7”，8.7和11.3微米）的主要（最强）条带，3200-2700 cm的次要条带和宽阔特征。 -1 [校正3200-2700-1]（3.1-3.7微米），1600-1100 cm-1（6.0-9微米）和910-770 cm-1（11-13微米）的区域以及振动区域准连续谱，涵盖整个中红外和有助于高频红外连续谱的电子跃迁。所有主要和次要乐队，以及准连续谱，可以归因于分子大小PAHs的振动跃迁。后两个广泛的特征可能来自非常大的PAH，PAH簇和无定形碳颗粒。星际光谱与实验室光谱的精确匹配尚不可能，因为实验室光谱无法获得星际介质中可能存在的形式的PAH（完全分离，电离，有些完全脱氢并包含约20至40个碳原子） ）。还详细描述了一种可以从振动激发的分子计算IR荧光光谱的方法。荧光带强度，弛豫率以及对分子大小和能量含量的依赖性均得到明确处理。对星际光谱的分析表明，主导红外光谱的多环芳烃含有约20至40个碳原子。将使用此方法获得的结果与使用热逼近获得的结果进行比较。结果表明，对于低频模式下的高水平振动激发和发射，两种方法得出的结果相似。但是，在低水平的振动激励下以及对于高频模式（例如3040 cm-1、3.3微米波段），热方法会高估发射强度。对于分子反应（如H损失，氘富集和碳骨架重排）的计算，热近似是无效的。提出了PAH分子与无定形碳颗粒之间的关系，并描述了它们在星壳中的产生。讨论了最可能的星际PAH分子结构，并详细考虑了与星际氧和氢原子发生破坏性反应的可能性，发现这种可能性并不重要。进行星际PAH大小和丰度估算。约百分之几的可用星际碳被束缚在较小的（20-40个碳原子）多环芳烃中，而PAH则具有鲜明的特征，而类似的数量被束缚在较大的（200-500个碳原子）中）PAH或PAH团簇和无定形碳颗粒，它们是构成1600-1100和900-770 cm-1（6-9和11-13微米）区域下方的广泛成分的原因。结果表明，在星际消光曲线的紫外线部分产生的这些多环芳烃和多环芳烃相关材料的光谱结构刚好低于电流检测极限，但落在哈勃太空望远镜可检测的范围内。最后，描述了PAH电荷对紫外线，可见光和红外线区域的影响。