Doddipatla Srinivas, Galimova Galiya R, Wei Hongji, Thomas Aaron M, He Chao, Yang Zhenghai, Morozov Alexander N, Shingledecker Christopher N, Mebel Alexander M, Kaiser Ralf I
Department of Chemistry, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA.
Department of Chemistry and Biochemistry, Florida International University, Miami, FL, 33199, USA.
Sci Adv. 2021 Jan 1;7(1). doi: 10.1126/sciadv.abd4044. Print 2021 Jan.
Polycyclic aromatic hydrocarbons (PAHs) are fundamental molecular building blocks of fullerenes and carbonaceous nanostructures in the interstellar medium and in combustion systems. However, an understanding of the formation of aromatic molecules carrying five-membered rings-the essential building block of nonplanar PAHs-is still in its infancy. Exploiting crossed molecular beam experiments augmented by electronic structure calculations and astrochemical modeling, we reveal an unusual pathway leading to the formation of indene (CH)-the prototype aromatic molecule with a five-membered ring-via a barrierless bimolecular reaction involving the simplest organic radical-methylidyne (CH)-and styrene (CHCH) through the hitherto elusive methylidyne addition-cyclization-aromatization (MACA) mechanism. Through extensive structural reorganization of the carbon backbone, the incorporation of a five-membered ring may eventually lead to three-dimensional PAHs such as corannulene (CH) along with fullerenes (C, C), thus offering a new concept on the low-temperature chemistry of carbon in our galaxy.
多环芳烃（PAHs）是星际介质和燃烧系统中富勒烯及碳质纳米结构的基本分子构建单元。然而，对于携带五元环的芳香分子（非平面PAHs的基本构建单元）的形成的理解仍处于起步阶段。通过利用结合电子结构计算和天体化学建模的交叉分子束实验，我们揭示了一条不同寻常的途径，该途径通过一种涉及最简单有机自由基亚甲基（CH）和苯乙烯（CHCH）的无势垒双分子反应，经由迄今难以捉摸的亚甲基加成-环化-芳构化（MACA）机制，导致茚（CH）的形成，茚是具有五元环的原型芳香分子。通过碳骨架的广泛结构重组，五元环的并入最终可能导致三维PAHs如碗烯（CH）以及富勒烯（C、C）的形成，从而为我们星系中碳的低温化学提供了一个新概念。
