On Polycyclic Aromatic Hydrocarbon Molecules in Comets

彗星中的多环芳烃分子

• 批准号: 1109039
• 负责人: Aigen Li
• 金额: $ 16.16万
• 依托单位: University of Missouri-Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1109039&HistoricalAwards=false
• 关键词: Polycyclic; Aromatic; Hydrocarbon; Molecules; Comets

This project is comprised of theoretical studies of the excitation, alteration, and destruction of the class of large organic molecules known as polycyclic aromatic hydrocarbons (PAHs). These molecules are detected by their characteristic spectra in observations of the interstellar medium (ISM) in our own Milky Way and other galaxies. Logically, they would have been present in the original material that formed our Solar System. But the fragility of PAH molecules implies that they would not have been expected to survive in Solar System bodies, except possibly in comets. Detecting PAHs in comets would establish an important chemical link between the ISM and the Solar System. PAHs have not been unambiguously detected in the observed infrared spectra of comets, in part because the expected infrared emission spectra and destruction rates of PAHs in cometary environments are not adequately understood. This is the problem that the proposal aims to address. The Principal Investigator and a supported graduate student will study the photoexcitation, photoionization, and photodissociation of PAH molecules and their ions in cometary comae illuminated by the Sun. They will calculate, using numerical statistical mechanics techniques, the emission spectra and destruction rates of 23 representative specific PAH molecules and their ions, as well as three nitrogen-substituted PAHs appropriate to nitrogen-rich comets and generic "astro-PAH" models approximating the interstellar species. The goal is to create a web-based "library" of the emission spectra and photodissociation and photoionization rates of PAH molecules as a function of distance from the Sun. By comparing observed cometary spectra the model spectra from the library, researchers will be able to constrain PAH production and destruction rates and interpret observational detections and non-detections.

该项目包括对称为多环芳烃 (PAH) 的大有机分子的激发、改变和破坏的理论研究。这些分子在我们银河系和其他星系的星际介质（ISM）观测中通过其特征光谱被检测到。从逻辑上讲，它们应该存在于形成我们太阳系的原始材料中。但多环芳烃分子的脆弱性意味着它们不会在太阳系天体中生存，除非可能在彗星中。检测彗星中的多环芳烃将在 ISM 和太阳系之间建立重要的化学联系。在观测到的彗星红外光谱中尚未明确检测到多环芳烃，部分原因是彗星环境中多环芳烃的预期红外发射光谱和破坏率尚未得到充分了解。这正是该提案旨在解决的问题。首席研究员和一名支持的研究生将研究太阳照射的彗星彗发中 PAH 分子及其离子的光激发、光离子化和光解离。他们将使用数值统计力学技术计算 23 种具有代表性的特定多环芳烃分子及其离子的发射光谱和破坏率，以及适合富氮彗星的三种氮取代多环芳烃和近似星际物种的通用“astro-PAH”模型。目标是创建一个基于网络的“库”，其中包含 PAH 分子的发射光谱以及光解离和光电离率与太阳距离的函数关系。通过将观测到的彗星光谱与库中的模型光谱进行比较，研究人员将能够限制多环芳烃的产生和破坏率，并解释观测到的检测和未检测到的情况。