Identification of the Elusive Methyl-Loss Channel in the Crossed Molecular Beam Study of Gas-Phase Reaction of Dicarbon Molecules (C2; X1Σg+/a3Πu) with 2-Methyl-1,3-butadiene (C5H8; X1A')

Medvedkov, Iakov A.; Yang, Zhenghai; Goettl, Shane J.; Kaiser, Ralf I.

doi:10.1021/acs.jpca.5c00639

Identification of the Elusive Methyl-Loss Channel in the Crossed Molecular Beam Study of Gas-Phase Reaction of Dicarbon Molecules (C₂; X¹Σ_g⁺/a³Π_u) with 2-Methyl-1,3-butadiene (C₅H₈; X¹A')

Journal Article · Fri Mar 28 00:00:00 EDT 2025 · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

DOI:https://doi.org/10.1021/acs.jpca.5c00639· OSTI ID:2565571

^[1]; Yang, Zhenghai ^[1]; ^[1]; ^[1]

University of Hawai‘i at Manoa, Honolulu, HI (United States)

The crossed molecular beams technique was utilized to explore the reaction of dicarbon C₂ (X¹Σ_g⁺/a³Π_u) with 2-methyl-1,3-butadiene (isoprene, CH₂C(CH₃)CHCH₂; X¹A') at a collision energy of 28 ± 1 kJ mol⁻¹ using a supersonic dicarbon beam generated via photolysis (248 nm) of helium-seeded tetrachloroethylene (C₂Cl₄). Here, experimental data combined with previous ab initio calculations provide evidence of the detection of the hitherto elusive methyl elimination channels leading to acyclic resonantly stabilized hexatetraenyl radicals: 1,2,4,5-hexatetraen-3-yl (CH₂CC•CHCCH₂) and/or 1,3,4,5-hexatetraen-3-yl (CH₂CHC•CCCH₂). These pathways are exclusive to the singlet potential energy surface, with the reaction initiated by the barrierless addition of dicarbon to one of the carbon-carbon double bonds in the diene. In combustion systems, both hexatetraenyl radicals can isomerize to the phenyl radical (C₆H₅) through a hydrogen atom assisted isomerization – the crucial reaction intermediate and molecular mass growth species step toward the formation of polycyclic aromatic hydrocarbons (PAHs) and soot.

View Accepted Manuscript (DOE)

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:: 2565571

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: 14 Vol. 129; ISSN 1089-5639

Publisher:: American Chemical SocietyCopyright Statement

Country of Publication:: United States

Language:: English

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Identification of the Elusive Methyl-Loss Channel in the Crossed Molecular Beam Study of Gas-Phase Reaction of Dicarbon Molecules (C2; X1Σg+/a3Πu) with 2-Methyl-1,3-butadiene (C5H8; X1A')

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Identification of the Elusive Methyl-Loss Channel in the Crossed Molecular Beam Study of Gas-Phase Reaction of Dicarbon Molecules (C₂; X¹Σ_g⁺/a³Π_u) with 2-Methyl-1,3-butadiene (C₅H₈; X¹A')