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Title: HACA's Heritage: A Free-Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars

The hydrogen-abstraction/acetylene-addition (HACA) mechanism has been central for the last decades in attempting to rationalize the formation of polycyclic aromatic hydrocarbons (PAHs) as detected in carbonaceous meteorites such as in Murchison. Nevertheless, the basic reaction mechanisms leading to the formation of even the simplest tricyclic PAHs like anthracene and phenanthrene are still elusive. By exploring the previously unknown chemistry of the ortho-biphenylyl radical with acetylene, we deliver compelling evidence on the efficient synthesis of phenanthrene in carbon-rich circumstellar environments. However, the lack of formation of the anthracene isomer implies that HACA alone cannot be responsible for the formation of PAHs in extreme environments. Considering the overall picture, alternative pathways such as vinylacetylene-mediated reactions are required to play a crucial role in the synthesis of complex PAHs in circumstellar envelopes of dying carbon-rich stars.
ORCiD logo [1] ; ORCiD logo [1] ;  [2] ;  [2] ; ORCiD logo [2] ; ORCiD logo [2] ;  [3] ;  [4] ;  [4]
  1. Univ. of Hawaii, Honolulu, HI (United States). Dept. of Chemistry
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
  3. Florida Intl Univ., Miami, FL (United States). Dept. of Chemistry and Biochemistry
  4. Samara National Research Univ. (Russian Federation). Dept. of Physics
Publication Date:
Grant/Contract Number:
AC02-05CH11231; FG02‐03ER15411; FG02‐04ER15570; 14.Y26.31.0020; FG02-03ER15411; FG02-04ER15570
Accepted Manuscript
Journal Name:
Angewandte Chemie (International Edition)
Additional Journal Information:
Journal Name: Angewandte Chemie (International Edition); Journal Volume: 56; Journal Issue: 16; Related Information: © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim; Journal ID: ISSN 1433-7851
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; Government of the Russian Federation
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 79 ASTRONOMY AND ASTROPHYSICS; circumstellar envelopes; gas phase chemistry; hydrogen-abstraction/acetylene-addition (HACA); mass spectrometry; polycyclic aromatic hydrocarbons
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1376753