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发挥着关键作用，并在生命的益生菌进化中发挥着关键作用。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非常重要。多环芳烃的红外特征--所谓的不明红外(UIR)发射波段--在我们的银河系和更远的地方无处不在。然而，排放人口的具体数字仍然难以捉摸。事实上，由于UIR谱带来自只涉及最近邻原子的化学键，它们对大小和结构的依赖性很弱，因此不可能识别导致红外发射的单个PAH分子。类似地，尽管已经确定PAH发射波段因物体而异，甚至在空间上也因物体而异，但这些变化的起源并不完全清楚。这些未知因素是开发诊断工具的主要障碍，这些工具将把无处不在的UIR波段转变为对宇宙中物理和化学条件的强大探测器。*我提出的研究计划通过使用天文观测和NASA Ames PAH红外光谱数据库对太空中的多环芳烃进行了几项创新的研究，以解决这些未知问题，该数据库包含了大量多环芳烃和相关分子的物理和光谱性质。特别是，我将描述各种天文天体中UIR波段的变化，并将这些变化与当地的物理条件进行比较，例如到激发源的距离、辐射场、电子密度和温度。然后，我将使用NASA Ames数据库来确定如何从多环芳烃的分子性质(例如大小、电荷)来理解这些变化。这将揭示多环芳烃如何与其环境的物理条件相互作用并反映出来。因此，这种观测方法将提供具有物理条件的多环芳烃特性的经验定量校准。这反过来将允许在近距离和远距离地区使用UIR波段作为环境诊断工具(例如，像气象站一样)。我还将利用这些研究来调查含碳物种的加工。特别是，我将调查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导致不同程度的芳香性和多环芳烃谱带的变化。

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.********