Random mixtures of polycyclic aromatic hydrocarbon spectra match interstellar infrared emission
Random mixtures of polycyclic aromatic hydrocarbon spectra match interstellar infrared emission
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DOI：
10.1051/0004-6361/201423953
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发表时间：
2014-05
影响因子：
6.5
通讯作者：
M. Rosenberg;O. Bern'e;C. Boersma
中科院分区：
文献类型：
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作者：
M. Rosenberg;O. Bern'e;C. Boersma
中红外（Mid-IR;在6.2、7.7、8.6、11.3和12.7 μm处，各种各样的天体的光谱（5-15 μm）都显示出一系列宽的发射特征。大约30年前，有人提出这些特征是由于一系列紫外线加热的纳米级碳质分子（称为多环芳烃（PAH））的发射，导致它们被称为芳香族IR带（AIB）。今天，接受PAH模型是远远没有解决，作为一个单一的PAH在太空中的识别尚未成功，和物理相关的理论模型，涉及真正的PAH横截面不再现AIB的细节。在本文中，我们使用的美国宇航局艾姆斯多环芳烃红外光谱数据库，其中包含超过500个量子计算的光谱，结合一个简单的排放模型，表明任何随机混合物产生的光谱至少30多环芳烃收敛到相同的内核光谱。该核谱捕捉了PAH发射谱的本质，并且与AIBs的观测高度相关，强烈支持PAH是其来源。此外，需要大量分子的事实意味着，对跨越可见光、近红外和远红外光谱区域的AIB有贡献的单个多环芳烃的光谱特征很弱，这解释了为什么它们尚未被检测到。一个改进的努力，加入多环芳烃排放过程的实验室，理论和观测研究，将支持使用多环芳烃功能作为探测物理和化学条件在近距离和远距离的宇宙。
The mid-infrared (mid-IR; 5–15 μm) spectrum of a wide variety of astronomical objects exhibits a set of broad emission features at 6.2, 7.7, 8.6, 11.3, and 12.7 μm. About 30 years ago it was proposed that these signatures are due to emission from a family of UV heated nanometer-sized carbonaceous molecules known as polycyclic aromatic hydrocarbons (PAHs), causing them to be referred to as aromatic IR bands (AIBs). Today, the acceptance of the PAH model is far from settled, as the identification of a single PAH in space has not yet been successful, and physically relevant theoretical models involving true PAH cross sections do not reproduce the AIBs in detail. In this paper, we use the NASA Ames PAH IR Spectroscopic Database, which contains over 500 quantum-computed spectra, in conjunction with a simple emission model, to show that the spectrum produced by any random mixture of at least 30 PAHs converges to the same kernel-spectrum. This kernel-spectrum captures the essence of the PAH emission spectrum and is highly correlated with observations of AIBs, strongly supporting PAHs as their source. Furthermore, the fact that a large number of molecules are required implies that spectroscopic signatures of the individual PAHs contributing to the AIBs spanning the visible, near-IR, and far-IR spectral regions are weak, explaining why they have not yet been detected. An improved effort, joining laboratory, theoretical, and observational studies of the PAH emission process, will support the use of PAH features as a probe of physical and chemical conditions in the near and distant Universe.