The PAH emission bands as a diagnostic tool

多环芳烃（PAHs）是在太空中发现的最大的有机分子之一，它们在各种物理和化学过程中起着至关重要的作用，在生命进化的过程中。因此，研究这些丰富的星际分子，它们的形成和演化，以及控制它们丰度的天体物理过程，对于理解我们的宇宙根源和我们周围的宇宙具有极其重要的意义。******多环芳烃的红外特征-所谓的不明红外（UIR）发射带-在我们的银河系和更远的地方无处不在。然而，排放人口的具体情况仍然难以捉摸。事实上，由于UIR波段来源于仅涉及最近邻原子的化学键，因此它们对大小和结构的依赖性很弱，因此不可能确定引起IR发射的单个多环芳烃分子。类似地，虽然可以确定多环芳烃的发射带在不同的物体之间甚至在物体内部都是不同的，但这些变化的起源并没有完全了解。这些未知因素是诊断工具开发的主要障碍，这些工具将把无处不在的UIR波段转化为对宇宙物理和化学条件的强大探测。******我提出的研究计划通过与NASA艾姆斯多环芳烃红外光谱数据库（包含大量多环芳烃及其相关分子的物理和光谱特性）相结合的天文观测，在太空中开展多环芳烃的几项创新研究，解决了这些未知问题。特别是，我将描述各种天文物体中UIR波段的变化，并将其与当地的物理条件进行比较，例如与激发源的距离，辐射场，电子密度和温度。然后，我将使用NASA Ames数据库来确定如何根据多环芳烃分子特性（例如大小，电荷）来理解这些变化。这将揭示多环芳烃如何与环境的物理条件相互作用和反映。因此，这种观测方法将提供物理条件下多环芳烃特征的经验定量校准。反过来，这将允许在远近地区使用UIR波段作为环境诊断工具（例如气象站）。我还将利用这些研究来研究碳质物种的加工。特别是，我将研究多环芳烃是否被加工成富勒烯和小碳氢化合物，以及紫外线处理是否会引起不同程度的芳香性和多环芳烃带谱的变化。********

Polycyclic Aromatic Hydrocarbons (PAHs) are among the largest organic molecules found in space, where they play a crucial role in various physical and chemical processes, and in the prebiotic evolution toward life. Hence, studying these abundant interstellar molecules, their formation and evolution, and the astrophysical processes that control their abundance is of tremendous importance to understand our cosmic roots and the Universe around us.******The infrared signature of PAHs - the so-called Unidentified Infrared (UIR) emission bands - is omnipresent in our Galaxy and beyond. However, specifics of the emitting population remain elusive. Indeed, since the UIR bands originate from chemical bonds involving only nearest-neighbor atoms, they have only a weak dependence on size and structure, and it is therefore not possible to identify the individual PAH molecules that cause the IR emission. Similarly, although it is firmly established that the PAH emission bands vary from object to object and even spatially within objects, the origin of these variations is not entirely understood. These unknowns are major roadblocks in the development of diagnostic tools that would transform the ubiquitous UIR bands into powerful probes of the physical and chemical conditions in the Universe. ******The research program I propose addresses these unknowns by carrying out several innovative studies of PAHs in space using astronomical observations in conjunction with the NASA Ames PAH IR spectral database, which contains the physical and spectral properties of a large number of PAHs and related molecules. In particular, I will characterize the variations of the UIR bands in a wide variety of astronomical objects and compare these to local physical conditions, such as distance from the exciting source, radiation field, electron density, and temperature. I will then use the NASA Ames database to determine how these variations can be understood in terms of PAH molecular properties (e.g. size, charge). This will reveal how PAHs interact with and reflect the physical conditions of their environment. This observational approach will thus provide an empirical quantitative calibration of the PAH characteristics with physical conditions. This, in turn, will allow using the UIR bands as an environmental diagnostic tool (e.g., like a weather station) in regions near and far. I will also use these studies to investigate the processing of carbonaceous species. In particular, I will investigate whether PAHs are processed into fullerenes and small hydrocarbons, as well as whether UV processing causes a varying degree of aromaticity and changes in the PAH band profiles.********