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On the formation and the isomer specific detection of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), and 1,3-butadiene (CH2CHCHCH2) from interstellar methane ice analogues

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Abstract

Pure methane (CH4) ices processed by energetic electrons under ultra-high vacuum conditions to simulate secondary electrons formed via galactic cosmic rays (GCRs) penetrating interstellar ice mantles have been shown to produce an array of complex hydrocarbons with the general formulae: CnH2n+2 (n = 4–8), CnH2n (n = 3–9), CnH2n−2 (n = 3–9), CnH2n−4 (n = 4–9), and CnH2n−6 (n = 6–7). By monitoring the in situ chemical evolution of the ice combined with temperature programmed desorption (TPD) studies and tunable single photon ionization coupled to a reflectron time-of-flight mass spectrometer, specific isomers of C3H4, C3H6, C4H4, and C4H6 were probed. These experiments confirmed the synthesis of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), 1-butyne (HCCC2H5), 2-butyne (CH3CCCH3), 1,2-butadiene (H2CCCH(CH3)), and 1,3-butadiene (CH2CHCHCH2) with yields of 2.17 ± 0.95 × 10−4, 3.7 ± 1.5 × 10−3, 1.23 ± 0.77 × 10−4, 1.28 ± 0.65 × 10−4, 4.01 ± 1.98 × 10−5, 1.97 ± 0.98 × 10−4, 1.90 ± 0.84 × 10−5, and 1.41 ± 0.72 × 10−4 molecules eV−1, respectively. Mechanistic studies exploring the formation routes of methylacetylene, propene, and vinylacetylene were also conducted, and revealed the additional formation of the 1,2,3-butatriene isomer. Several of the above isomers, methylacetylene, propene, vinylacetylene, and 1,3-butadiene, have repeatedly been shown to be important precursors in the formation of polycyclic aromatic hydrocarbons (PAHs), but until now their interstellar synthesis has remained elusive.

Graphical abstract: On the formation and the isomer specific detection of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), and 1,3-butadiene (CH2CHCHCH2) from interstellar methane ice analogues

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Publication details

The article was received on 21 Jun 2018, accepted on 30 Aug 2018 and first published on 30 Aug 2018


Article type: Paper
DOI: 10.1039/C8CP03921F
Citation: Phys. Chem. Chem. Phys., 2019, Advance Article
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    On the formation and the isomer specific detection of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), and 1,3-butadiene (CH2CHCHCH2) from interstellar methane ice analogues

    M. J. Abplanalp, S. Góbi and R. I. Kaiser, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C8CP03921F

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