Zhao Long, Xu Bo, Ablikim Utuq, Lu Wenchao, Ahmed Musahid, Evseev Mikhail M, Bashkirov Eugene K, Azyazov Valeriy N, Howlader A Hasan, Wnuk Stanislaw F, Mebel Alexander M, Kaiser Ralf I
Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, 96822, USA.
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Chemphyschem. 2019 Mar 18;20(6):791-797. doi: 10.1002/cphc.201801154. Epub 2019 Feb 13.
For the last decades, the hydrogen-abstraction-acetylene-addition (HACA) mechanism has been widely invoked to rationalize the high-temperature synthesis of PAHs as detected in carbonaceous meteorites (CM) and proposed to exist in the interstellar medium (ISM). By unravelling the chemistry of the 9-phenanthrenyl radical ([C H ] ) with vinylacetylene (C H ), we present the first compelling evidence of a barrier-less pathway leading to a prototype tetracyclic PAH - triphenylene (C H ) - via an unconventional hydrogen abstraction-vinylacetylene addition (HAVA) mechanism operational at temperatures as low as 10 K. The barrier-less, exoergic nature of the reaction reveals HAVA as a versatile reaction mechanism that may drive molecular mass growth processes to PAHs and even two-dimensional, graphene-type nanostructures in cold environments in deep space thus leading to a better understanding of the carbon chemistry in our universe through the untangling of elementary reactions on the most fundamental level.
在过去几十年里，氢抽取-乙炔加成（HACA）机制被广泛用于解释在碳质陨石（CM）中检测到的多环芳烃（PAH）的高温合成，并被认为存在于星际介质（ISM）中。通过揭示9-菲基自由基（[C₁₄H₉]）与乙烯基乙炔（C₄H₄）的化学反应，我们首次提供了令人信服的证据，证明存在一条无障碍途径，该途径通过一种在低至10 K的温度下运行的非常规氢抽取-乙烯基乙炔加成（HAVA）机制，生成原型四环多环芳烃——三亚苯（C₁₈H₁₂）。该反应的无障碍、放能性质表明HAVA是一种通用的反应机制，它可能在深冷宇宙环境中推动分子质量增长过程，形成多环芳烃甚至二维石墨烯型纳米结构，从而通过在最基本层面上解开基本反应，更好地理解我们宇宙中的碳化学。
