具有天体化学意义的复杂有机物质的远红外和中红外光谱学：煤、重石油馏分和沥青质
Far- and mid-infrared spectroscopy of complex organic matter of astrochemical interest: coal, heavy petroleum fractions, and asphaltenes
摘要：
多种分子种类的共存（即，芳族、脂环族和脂族）表明未识别的IR发射（UIE）发生于含有芳族和脂族结构混合物的小固体颗粒（例如，煤、石油等），重新唤起了天文学家对这类物质的兴趣。一系列的重石油馏分，即DAE，RAE，BQ-1，和沥青质从BQ-1衍生的无烟煤和沥青一起被用来作为模型化合物在匹配的带模式的发射特征的原行星状星云（PPNe）。在中红外波段（2.5-16.7 μ m）和远红外波段（16.7-200 μ m）对所有模型材料进行了检测，并与PPNe的UIE谱带进行了比较。BQ-1重质芳烃油馏分和沥青质馏分的PPNe谱带最匹配。特别令人感兴趣的是BQ-1的能力，以配合带模式的芳香族-脂肪族C-H伸缩带的某些PPNe，这是没有实现的结果，无论是由煤模型，也没有通过其他石油馏分在这里考虑。该研究表明，PPNe的发射特性的一个新的有趣的分子模型是沥青质分子，其由包含3-4个稠合芳环的芳族核被脂环族（环烷烃）和脂肪族烷基链包围组成。相反，它示出了涉及多环芳烃的混合物的模型建模的芳香族红外发射带的弱点。这些复杂有机化合物的实验室光谱代表了天文界具有高价值的独特数据集;例如，它们可以与赫歇尔空间天文台光谱（~51-220 μ m）的几个天体物理环境，如（原）PNe、H II区、反射星云、恒星形成星系和年轻恒星天体进行比较。
英文摘要：
The coexistence of a large variety of molecular species (i.e., aromatic, cycloaliphatic and aliphatic) in several astrophysical environments suggests that unidentified IR emission (UIE) occurs from small solid particles containing a mix of aromatic and aliphatic structures (e.g., coal, petroleum, etc.), renewing the astronomical interest on this type of materials. A series of heavy petroleum fractions namely DAE, RAE, BQ-1, and asphaltenes derived from BQ-1 were used together with anthracite coal and bitumen as model compounds in matching the band pattern of the emission features of proto-planetary nebulae (PPNe). All the model materials were examined in the mid-infrared (2.5-16.7 um) and for the first time in the far-infrared (16.7-200 um), and the IR bands were compared with the UIE from PPNe. The best match of the PPNe band pattern is offered by the BQ-1 heavy aromatic oil fraction and by its asphaltenes fraction. Particularly interesting is the ability of BQ-1 to match the band pattern of the aromatic-aliphatic C-H stretching bands of certain PPNe, a result which is not achieved neither by the coal model nor by the other petroleum fractions considered here. This study shows that a new interesting molecular model of the emission features of PPNe are asphaltene molecules which are composed by an aromatic core containing 3-4 condensed aromatic rings surrounded by cycloaliphatic (naphtenic) and aliphatic alkyl chains. It is instead shown the weakness of the model involving a mixture of PAHs for modeling the aromatic IR emission bands. The laboratory spectra of these complex organic compounds represent a unique data set of high value for the astronomical community; e.g., they may be compared with the Herschel Space Observatory spectra (~51-220 um) of several astrophysical environments such as (proto-) PNe, H II regions, reflection nebulae, star forming galaxies, and young stellar objects.
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