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Reaction Dynamics in Astrochemistry: Low-Temperature Pathways to Polycyclic Aromatic Hydrocarbons in the Interstellar Medium

Journal Article · · Annual Review of Physical Chemistry
 [1];  [2];  [3]
  1. Univ. of Hawaii at Manoa, Honolulu, HI (United States); University of Hawaii at Manoa
  2. Univ. of Hawaii at Manoa, Honolulu, HI (United States)
  3. Florida International Univ., Miami, FL (United States)

Bimolecular reactions of phenyl-type radicals with the C4 and C5 hydrocarbons vinylacetylene and (methyl-substituted) 1,3-butadiene have been found to synthesize polycyclic aromatic hydrocarbons (PAHs) with naphthalene and 1,4-dihydronaphthalene cores in exoergic and entrance barrierless reactions under single-collision conditions. The reaction mechanism involves the initial formation of a van der Waals complex and addition of a phenyl-type radical to the C1 position of a vinyl-type group through a submerged barrier. Investigations suggest that in the hydrocarbon reactant, the vinyl-type group must be in conjugation with a –C≡CH or –HC=CH2 group to form a resonantly stabilized free radical intermediate, which eventually isomerizes to a cyclic intermediate followed by hydrogen loss and aromatization (PAH formation). Finally, the vinylacetylene-mediated formation of PAHs might be expanded to more complex PAHs, such as anthracene and phenanthrene, in cold molecular clouds via barrierless reactions involving phenyl-type radicals, such as naphthyl, which cannot be accounted for by the classical hydrogen abstraction–acetylene addition mechanism.

Research Organization:
Univ. of Hawaii at Manoa, Honolulu, HI (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
FG02-03ER15411; FG02-04ER15570
OSTI ID:
1602874
Journal Information:
Annual Review of Physical Chemistry, Journal Name: Annual Review of Physical Chemistry Journal Issue: 1 Vol. 66; ISSN 0066-426X
Publisher:
Annual ReviewsCopyright Statement
Country of Publication:
United States
Language:
English

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