Jump to main content
Jump to site search

Issue 16, 2018
Previous Article Next Article

A combined crossed molecular beams and computational study on the formation of distinct resonantly stabilized C5H3 radicals via chemically activated C5H4 and C6H6 intermediates

Author affiliations

Abstract

The crossed molecular beams technique was utilized to explore the formation of three isomers of resonantly stabilized (C5H3) radicals along with their d2-substituted counterparts via the bimolecular reactions of singlet/triplet dicarbon [C2(X1Σ+g/a3Πu)] with methylacetylene [CH3CCH(X1A1)], d3-methylacetylene [CD3CCH(X1A1)], and 1-butyne [C2H5CCH(X1A′)] at collision energies up to 26 kJ mol−1via chemically activated singlet/triplet C5H4/C5D3H and C6H6 intermediates. These studies exploit a newly developed supersonic dicarbon [C2(X1Σ+g/a3Πu)] beam generated via photolysis of tetrachloroethylene [C2Cl4(X1Ag)] by excluding interference from carbon atoms, which represent the dominating (interfering) species in ablation-based dicarbon sources. We evaluated the performance of the dicarbon [C2(X1Σ+g/a3Πu)] beam in reactions with methylacetylene [CH3CCH(X1A1)] and d3-methylacetylene [CD3CCH(X1A1)]; the investigations demonstrate that the reaction dynamics match previous studies in our laboratory utilizing ablation-based dicarbon sources involving the synthesis of 1,4-pentadiynyl-3 [HCCCHCCH(X2B1)] and 2,4-pentadiynyl-1 [H2CCCCCH(X2B1)] radicals via hydrogen (deuterium) atom elimination. Considering the C2(X1Σ+g/a3Πu)–1-butyne [C2H5CCH(X1A′)] reaction, the hitherto elusive methyl-loss pathway was detected. This channel forms the previously unknown resonantly stabilized penta-1-yn-3,4-dienyl-1 [H2CCCHCC(X2A)] radical along with the methyl radical [CH3(X2A2′′)] and is open exclusively on the triplet surface with an overall reaction energy of −86 ± 10 kJ mol−1. The preferred reaction pathways proceed first by barrierless addition of triplet dicarbon to the π-electronic system of 1-butyne, either to both acetylenic carbon atoms or to the sterically more accessible carbon atom, to form the methyl-bearing triplet C6H6 intermediates [i41b] and [i81b], respectively, with the latter decomposing via a tight exit transition state to penta-1-yn-3,4-dienyl-1 [(H2CCCHCC(X2A)] plus the methyl radical [CH3(X2A2′′)]. The successful unraveling of this methyl-loss channel – through collaborative experimental and computational efforts – underscores the viability of the photolytically generated dicarbon beam as an unprecedented tool to access reaction dynamics underlying the formation of resonantly stabilized free radicals (RSFR) that are vital to molecular mass growth processes that ultimately lead to polycyclic aromatic hydrocarbons (PAHs).

Graphical abstract: A combined crossed molecular beams and computational study on the formation of distinct resonantly stabilized C5H3 radicals via chemically activated C5H4 and C6H6 intermediates

Back to tab navigation

Supplementary files

Publication details

The article was received on 17 Jan 2018, accepted on 08 Mar 2018 and first published on 08 Mar 2018


Article type: Paper
DOI: 10.1039/C8CP00357B
Citation: Phys. Chem. Chem. Phys., 2018,20, 10906-10925
  •   Request permissions

    A combined crossed molecular beams and computational study on the formation of distinct resonantly stabilized C5H3 radicals via chemically activated C5H4 and C6H6 intermediates

    A. M. Thomas, M. Lucas, L. Zhao, J. Liddiard, R. I. Kaiser and A. M. Mebel, Phys. Chem. Chem. Phys., 2018, 20, 10906
    DOI: 10.1039/C8CP00357B

Search articles by author

Spotlight

Advertisements