Department of Physics, Faculty of Science, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
Nature. 2011 Oct 26;479(7371):80-3. doi: 10.1038/nature10542.
Unidentified infrared emission bands at wavelengths of 3-20 micrometres are widely observed in a range of environments in our Galaxy and in others. Some features have been identified as the stretching and bending modes of aromatic compounds, and are commonly attributed to polycyclic aromatic hydrocarbon molecules. The central argument supporting this attribution is that single-photon excitation of the molecule can account for the unidentified infrared emission features observed in 'cirrus' clouds in the diffuse interstellar medium. Of the more than 160 molecules identified in the circumstellar and interstellar environments, however, not one is a polycyclic aromatic hydrocarbon molecule. The detections of discrete and broad aliphatic spectral features suggest that the carrier of the unidentified infrared emission features cannot be a pure aromatic compound. Here we report an analysis of archival spectroscopic observations and demonstrate that the data are most consistent with the carriers being amorphous organic solids with a mixed aromatic-aliphatic structure. This structure is similar to that of the organic materials found in meteorites, as would be expected if the Solar System had inherited these organic materials from interstellar sources.
在我们银河系和其他星系的一系列环境中，广泛观察到波长为 3-20 微米的未识别红外发射带。一些特征已被确定为芳香族化合物的伸缩和弯曲模式，通常归因于多环芳烃分子。支持这种归属的主要论点是，分子的单光子激发可以解释在弥漫星际介质中的“卷云”云中观察到的未识别红外发射特征。然而，在恒星周围和星际环境中识别出的 160 多种分子中，没有一种是多环芳烃分子。离散和宽的脂肪族光谱特征的检测表明，未识别红外发射特征的载体不可能是纯芳香族化合物。在这里，我们报告了对档案光谱观测的分析，并证明数据与载体最一致，这些载体是具有混合芳族-脂肪族结构的无定形有机固体。这种结构类似于陨石中发现的有机材料，如果太阳系从星际源继承了这些有机材料，那么这种结构是可以预期的。
