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A Combined Crossed Molecular Beam and Theoretical Investigation of the Elementary Reaction of Tricarbon (C3(X1Σg+)) with Diacetylene (C4H2(X1Σg+)): Gas Phase Formation of the Heptatriynylidyne Radical (l-C7H(X2Π))

Journal Article · · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
 [1];  [2];  [1];  [1];  [2];  [3];  [4];  [1]
  1. University of Hawai‘i at Manoa, Honolulu, HI (United States)
  2. Samara National Research University (Russia)
  3. Ruhr-Universität Bochum (Germany)
  4. Florida International University, Miami, FL (United States)
+ Show Author Affiliations

An elucidation of the underlying formation pathways to acyclic hydrocarbons such as polyynes (CnH2), cumulenes (CnH2), and linear resonantly stabilized linear radicals (l-CnH) is indispensable to understand the hydrocarbon chemistry in extreme low and high temperature environments. In this study, we exploited the crossed molecular beam technique to investigate the reaction of tricarbon C3(X1Σg+) with diacetylene (butadiyne; HCCCCH; X1Σg+) at a collision energy of 47 ± 1 kJ mol⁻1. The experimental data were merged with ab initio calculations of the singlet C7H2 potential energy surface (PES) revealing that the reaction is initiated via the formation of an initial van der Waals reactant complex in the entrance channel. Subsequent rearrangements lead to various carbene-type and cyclic intermediates via ring-opening, ring-closure, and hydrogen migration processes eventually forming acyclic C7H2 isomers prior to their barrierless unimolecular decomposition to the most stable linear isomer, heptatriynylidyne (C7H, X2Π) in an overall endoergic reaction (+57 kJ mol⁻1). The reaction exhibits strong similarities to the tricarbon – acetylene (C3 – C2H2). Furthermore, the significant energy threshold suggests that the tricarbon reaction with (poly)acetylenes forming resonantly stabilized linear radicals are open in high-temperature environments such as combustion flames and circumstellar envelopes of carbon stars and planetary nebulae as their descendants; however, these reactions are closed in low-temperature environments as in cold molecular clouds and hydrocarbon-rich atmospheres of planets and their moons such as in Titan.

Research Organization:
University of Hawai‘i at Manoa, Honolulu, HI (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
FG02-03ER15411
OSTI ID:
2565572
Journal Information:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Journal Name: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory Journal Issue: 17 Vol. 129; ISSN 1089-5639
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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