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状分子，以及小的多环芳烃（PAH）代表了射电天文学在寒冷的黑暗分子云中明确识别的最复杂的分子，但对它们如何在星际条件下形成知之甚少。 使用实验和计算相结合的方法，该研究项目将研究在寒冷的星际云中形成复杂环状烃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烃的存在。 该项目将在先进的实验室天体物理学方法方面培训一名研究生，并为一名本科生提供研究机会。该研究小组将研究两种自由基物种，邻苯炔和2，3-吡啶的反应性。研究人员已经表明，最近在金牛座分子云（TMC-1）中发现的分子邻苯炔在合成复杂的烃乙炔基环戊二烯和茚中起着至关重要的作用，这些烃也在那里被发现。 本项目将在上述工作的基础上，研究可能形成PAH萘的邻苯炔和2，3-吡啶的反应，以及在TMC-1中检测到的氰基环戊二烯。 一个热解微反应器耦合到一个双成像光电子光离子符合（i2 PEPICO）光谱仪连接到真空紫外光束线的同步加速器将在研究中使用。 i2 PEPICO系统将能够测量-具有异构体特异性-在选定的自由基种类的化学反应中形成的产物。 势能面的量子化学计算将产生对反应的深入了解，并将采用统计模型来推导产物的支化分数。 由于研究的反应有可能产生在空间探测的可能候选产物，因此这项研究的结果也将指导未来的射电天文观测。 除了天文学之外，该项目的结果还可直接应用于燃烧化学中的PAH和烟尘形成机制。该奖项反映了NSF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.