Pyrene synthesis in circumstellar envelopes and its role in the formation of 2D nanostructures

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For the past decades, the hydrogen-abstraction/acetylene-addition (HACA) mechanism has been instrumental in attempting to untangle the origin of polycyclic aromatic hydrocarbons (PAHs) as identified in carbonaceous meteorites such as Allende and Murchison. However, the fundamental reaction mechanisms leading to the synthesis of PAHs beyond phenanthrene (C14H10) are still unknown. By exploring the reaction of the 4-phenanthrenyl radical (C14H9) with acetylene (C2H2) under conditions prevalent in carbon-rich circumstellar environments, we show evidence of a facile, isomer-selective formation of pyrene (C16H10). Along with the hydrogen-abstraction/vinylacetylene-addition (HAVA) mechanism, molecular mass growth processes from pyrene may lead through systematic ring expansions not only to more complex PAHs, but ultimately to 2D graphene-type structures. These fundamental reaction mechanisms are crucial to facilitate an understanding of the origin and evolution of the molecular universe and, in particular, of carbon in our Galaxy.

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This work was supported by the US Department of Energy, Basic Energy Sciences DE-FG02-03ER15411 (experimental studies), DE-FG02-04ER15570 (computational studies) and DE-SC0010409 (synthesis of precursor molecules) to the University of Hawaii, to Florida International University, and the University of California Berkeley, respectively. M.A., U.A., B.X. and the experiments at the chemical dynamics beamline at the ALS were supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231, through the Gas Phase Chemical Physics Program, Chemical Sciences Division. D.J. acknowledges support through a National Science Foundation Graduate Research Fellowship under grant no. DGE-1106400. The authors also thank X. Tielens (University of Leiden, The Netherlands) for helpful discussions.

Author information


  1. Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI, USA

    • Long Zhao
    •  & Ralf I. Kaiser
  2. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    • Bo Xu
    • , Utuq Ablikim
    •  & Musahid Ahmed
  3. Department of Chemistry, University of California, Berkeley, CA, USA

    • Dharati Joshi
    • , Gregory Veber
    •  & Felix R. Fischer
  4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    • Felix R. Fischer
  5. Kavli Energy Nano Sciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    • Felix R. Fischer
  6. Department of Chemistry and Biochemistry, Florida International University, Miami, FL, USA

    • Alexander M. Mebel


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D.J. and G.V. synthesized the molecular precursor; L.Z., B.X. and U.A. carried out the experimental measurements; L.Z. performed the data analysis; A.M.M. carried out the theoretical analysis; R.I.K., A.M.M. and M.A. discussed the data; F.R.F. supervised the synthesis of the molecular precursor; and R.I.K. designed the experiments and wrote the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Ralf I. Kaiser.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–11, Supplementary Table 1, Supplementary text