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

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.

On the formation of nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) in circumstellar and interstellar environments

The chemical evolution of extraterrestrial environments leads to the formation of nitrogen substituted polycyclic aromatic hydrocarbons (NPAHs) via gas phase radical mediated aromatization reactions.

Oxidation of the para-Tolyl Radical by Molecular Oxygen under Single-Collison Conditions: Formation of the para-Toloxy Radical

Crossed molecular beam experiments were performed to elucidate the chemical dynamics of the para-tolyl (CH₃C₆H₄) radical reaction with molecular oxygen (O₂) at an average collision energy of 35.3 ± 1.4 kJ mol^-1. Combined with theoretical calculations, the results show that para-tolyl is efficiently oxidized by molecular oxygen to para-toloxy (CH₃C₆H₄O) plus ground-state atomic oxygen via a complex forming, overall exoergic reaction (experimental, -33 ± 16 kJ mol^-1; computational, -42 ± 8 kJ mol^-1). The reaction dynamics are analogous to those observed for the phenyl (C₆H₅) plus molecular oxygen system which suggests the methyl group is a spectator during para-tolyl oxidation and that application of phenyl thermochemistry and reaction rates to para-substituted aryls is likely a suitable approximation.