Laboratory investigation of the gas-phase formation of (poly)cyclic hydrocarbons under interstellar conditions

由五个或六个碳原子组成的环分子，以及小的多环芳烃（PAHs）代表了射电天文学在寒冷黑暗的分子云中明确识别的最复杂的分子，但对于它们是如何在星际条件下形成的知之甚少。采用实验和计算相结合的方法，该研究项目将研究驱动冷星际云中复杂环状碳氢化合物形成的关键气相反应机制。该项目的结果将作为天体化学模型的关键输入，使天文学家能够解释太空中复杂环状碳氢化合物的存在。本项目将训练一名研究生掌握先进实验室天体物理学的方法，并为一名本科生提供研究机会。研究小组将研究邻苯和2,3-吡啶两种自由基的反应性。研究人员已经证明，最近在金牛座分子云（TMC-1）中发现的一种分子邻苯，在合成复杂碳氢化合物乙基环戊二烯和茚的过程中起着至关重要的作用，这两种化合物也在金牛座分子云中发现。本项目将以这项工作为基础，调查可能形成多环芳烃萘的邻苯和2,3-吡啶的反应，以及在TMC-1中检测到的氰环戊二烯。采用热解微反应器与同步加速器真空紫外光束线连接的双成像光电子光离子重合（i2PEPICO）光谱仪耦合。i2PEPICO系统将能够测量-具有异构体特异性-在选定的自由基种的化学反应中形成的产物。势能表面的量子化学计算将产生对反应的深入了解，统计模型将用于推导产物分支分数。由于所研究的反应有可能产生在太空中探测到的合理候选产物，因此这项研究的结果也将指导未来的射电天文观测。除天文学外，该项目的研究结果还可直接应用于燃烧化学中多环芳烃和烟尘形成机理的研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Cyclic molecules composed of five or six carbon atoms, as well as small polycyclic aromatic hydrocarbons (PAHs) represent the most complex molecules unambiguously identified by radio astronomy in cold dark molecular clouds, but little is known about how they are formed under interstellar conditions. Using a combined experimental and computational approach, this research project will investigate key gas phase reaction mechanisms driving the formation of complex cyclic hydrocarbons in cold interstellar clouds. Results from the project will serve as critical input to astrochemical models, allowing astronomers to explain the presence of complex cyclic hydrocarbons in space. This project will train a graduate student in methods of advanced laboratory astrophysics and provide research opportunities to an undergraduate student. The research team will investigate the reactivity of two radical species, ortho-benzyne and 2,3-pyridyne. The investigators have shown that ortho-benzyne, a molecule recently identified in the Taurus Molecular Cloud (TMC-1), plays a crucial role in the synthesis of the complex hydrocarbons ethynylcyclopentadiene and indene which have also been identified there. This project will build upon that work by investigating reactions of ortho-benzyne and 2,3-pyridyne that potentially form the PAH naphthalene, as well as the cyanocyclopentadienes which have been detected in TMC-1. A pyrolysis microreactor coupled to a double imaging photoelectron photoion coincidence (i2PEPICO) spectrometer connected to the vacuum ultraviolet beamline of a synchrotron will be used in the study. The i2PEPICO system will be capable of measuring---with isomer specificity---the products formed in chemical reactions of the selected radical species. Quantum chemical calculations of potential energy surfaces will yield insights into the reactions and a statistical model will be employed to derive product branching fractions. Because the reactions investigated have the potential to yield products that are plausible candidates for detection in space, results from this study would also guide future radio astronomical observations. Besides astronomy, results from this project are directly applicable to PAH and soot formation mechanisms in combustion chemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.