RESUMO
The fundamental reaction pathways to the simplest dialkylsubstituted aromatics-xylenes (C6 H4 (CH3 )2 )-in high-temperature combustion flames and in low-temperature extraterrestrial environments are still unknown, but critical to understand the chemistry and molecular mass growth processes in these extreme environments. Exploiting crossed molecular beam experiments augmented by state-of-the-art electronic structure and statistical calculations, this study uncovers a previously elusive, facile gas-phase synthesis of xylenes through an isomer-selective reaction of 1-propynyl (methylethynyl, CH3 CC) with 2-methyl-1,3-butadiene (isoprene, C5 H8 ). The reaction dynamics are driven by a barrierless addition of the radical to the diene moiety of 2-methyl-1,3-butadiene followed by extensive isomerization (hydrogen shifts, cyclization) prior to unimolecular decomposition accompanied by aromatization via atomic hydrogen loss. This overall exoergic reaction affords a preparation of xylenes not only in high-temperature environments such as in combustion flames and around circumstellar envelopes of carbon-rich Asymptotic Giant Branch (AGB) stars, but also in low-temperature cold molecular clouds (10â K) and in hydrocarbon-rich atmospheres of planets and their moons such as Triton and Titan. Our study established a hitherto unknown gas-phase route to xylenes and potentially more complex, disubstituted benzenes via a single collision event highlighting the significance of an alkyl-substituted ethynyl-mediated preparation of aromatic molecules in our Universe.
RESUMO
The D1-methanimine molecule (CHDNH; X1A')âthe simplest (deuterated) imineâhas been prepared through the elementary reaction of the D1-methylidyne (CD; X2Π) with ammonia (NH3; X1A1) under single collision conditions. As a highly reactive species with a carbon-nitrogen double bond and a key building block of biomolecules such as amino acids and nucleobases, methanimine is of particular significance in coupling the nitrogen and carbon chemistries in the interstellar medium and in hydrocarbon-rich atmospheres of planets and their moons. However, the underlying formation mechanisms of methanimine in these extreme environments are still elusive. The directed, low-temperature gas-phase formation of D1-methanimine will deepen our fundamental understanding of low-temperature molecular growth processes via carbon-nitrogen bond coupling. Considering the recent detection of the interstellar D1-methylidyne radical, the investigation of the CD-NH3 system also suggests a promising pathway for future astronomical observations of D1-methanimine as a molecular tracer of gas phase deuterium enrichment in deep space.
RESUMO
Unravelling the generation of complex organic molecules (COMs) on interstellar nanoparticles (grains) is essential in establishing predictive astrochemical reaction networks and recognizing evolution stages of molecular clouds and star-forming regions. The formation of COMs has been associated with the irradiation of interstellar ices by ultraviolet photons and galactic cosmic rays. Herein, we pioneer the first incorporation of synchrotron vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry (SVUV-PI-ReTOF-MS) in laboratory astrophysics simulation experiments to afford an isomer-selective identification of key COMs (ketene (H2CâCO); acetaldehyde (CH3CHO); vinyl alcohol (H2CâCHOH)) based on photoionization efficiency (PIE) curves of molecules desorbing from exposed carbon monoxide-methane (CO-CH4) ices. Our results demonstrate that the SVUV-PI-ReTOF-MS approach represents a versatile, rapid methodology for a comprehensive identification and explicit understanding of the complex organics produced in space simulation experiments. This methodology is expected to significantly improve the predictive nature of astrochemical models of complex organic molecules formed abiotically in deep space, including biorelated species linked to the origins-of-life topic.