EXPLOITING TUNABLE VACUUM ULTRAVIOLET PHOTOIONIZATION COMBINED WITH REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY FOR THE ISOMER-SPECIFIC DETECTION OF COMPLEX ORGANIC MOLECULES FORMED VIA INTERACTION OF IONIZING RADIATION WITH MIXED ASTROPHYSICAL ICE ANALOG

Over 200 molecules have been detected in the interstellar medium (ISM) with close to one third considered to be complex organic molecules (COMs), molecules containing six or more atoms. Gas-phase reaction networks of ion-molecule and neutral-neutral reactions have aided in the understanding of the evolution of the interstellar medium (ISM). However, these models fail to explain the synthesis of ubiquitous COMs with predicted abundances several orders of magnitude lower compared to observations in the ISM, such as in Sagittarius B2. Over the last decades astrophysical laboratory simulation experiments have shown that some of these COMs are formed via interaction of ionizing radiation within simple ices deposited on interstellar dust particles at $10\,$K (\ce{H2O}, \ce{CH3OH}, CO, \ce{CO2}, \ce{CH4}, \ce{NH3}). After processing the ice temperature programmed desorption was utilized to sublime the ice along with its newly formed products for analysis with single photon vacuum ultraviolet ionization coupled with a reflectron time-of-flight mass spectrometer (PI-ReTOF-MS). The use of PI-ReTOF-MS allows for the selective ionization and identification of structural isomers of COMs. Here, we report that the key COMs propynal (HCCCHO) and cyclopropenone (\ce{c-C3H2O}), which have both been detected in the ISM, can be synthesized within interstellar ices containing carbon monoxide (CO) and acetylene (\ce{C2H2}) at temperatures as low as $5\,$K. This is accomplished via non-equilibrium chemistry induced by the energetic electrons simulating those produced by galactic cosmic rays penetrating interstellar ices. Furthermore, cyclic COMs may act as tracers for non-equilibrium chemical processes at $10\,$K involving electronically excited reactants such as acetylene in excited triplet state(s). The incorporation of solid state data from these experiments, such as yield, branching ratio, and chemical and temperature conditions, into astrochemical models accounting for non-equilibrium has been shown to greatly improve predicted abundances

FORMATION OF THE BIORELEVANT MOLECULE PYRUVIC ACID IN INTERSTELLAR ANALOG ICES

More than 200 molecules have so far been detected in the interstellar medium (ISM), of which close to one third are complex organic molecules containing six or more atoms. Over the last decades, laboratory experiments simulating the conditions in cold molecular clouds have demonstrated that these COMs can form from interaction of ionizing radiation with simple ices deposited on interstellar dust particles (H$_2$O, CO, CO$_2$, CH$_3$OH, HCO, CH$_4$, NH$_3$). These experiments have unveiled multiple pathways towards the formation of acetaldehyde (CH$_3$CHO) in such ices, explaining its detection in many interstellar and circumstellar environments including tentative detections in interstellar ices. By condensing acetaldehyde and carbon monoxide at 5 K and irradiating the ice with 5 keV electrons, we simulate secondary electrons generated in the trace of galactic cosmic rays interacting with ices around cosmic dust particles. Combined infrared and photoionization reflectron time-of-flight mass spectrometry studies were employed to unambiguously identify pyruvic acid as reaction product from the irradiation by a barrierless radical-radical reaction of the acetyl (CH$_3$CO) and hydroxycarbonyl (HOCO) radicals. These results present an abiotic pathway towards the formation of this prebiotic molecule in the interstellar medium. As molecular clouds eventually collapse into a star-forming region, molecules formed in the ices can be incorporated into matter in the circumstellar disks, in which planets, planetoids, and comets can form. Fractions of these molecule can survive on their parent bodies to eventually be delivered to planets upon impact, presenting an exogenous source of prebiotic molecules on Earth. Among these, pyruvic acid constitutes a key starting material for the Krebs cycle, which supplies living organisms with energy. Furthermore, it may serve as a prebiotic building block for important biological compounds such as lactic acid or alanine

Synthesis of methanediol [CH2(OH)2]: The simplest geminal diol

Geminal diols—organic molecules carrying two hydroxyl groups at the same carbon atom—have been recognized as key reactive intermediates by the physical (organic) chemistry and atmospheric science communities as fundamental transients in the aerosol cycle and in the atmospheric ozonolysis reaction sequence. Anticipating short lifetimes and their tendency to fragment to water plus the aldehyde or ketone, free geminal diols represent one of the most elusive classes of organic reactive intermediates. Here, we afford an exceptional glance into the preparation of the previously elusive methanediol [CH2(OH)2] transient—the simplest geminal diol—via energetic processing of low-temperature methanol–oxygen ices. Methanediol was identified in the gas phase upon sublimation via isomer-selective photoionization reflectron time-of-flight mass spectrometry combined with isotopic substitution studies. Electronic structure calculations reveal that methanediol is formed via excited state dynamics through insertion of electronically excited atomic oxygen into a carbon–hydrogen bond of the methyl group of methanol followed by stabilization in the icy matrix. The first preparation and detection of methanediol demonstrates its gas-phase stability as supported by a significant barrier hindering unimolecular decomposition to formaldehyde and water. These findings advance our perception of the fundamental chemistry and chemical bonding of geminal diols and signify their role as an efficient sink of aldehydes and ketones in atmospheric environments eventually coupling the atmospheric chemistry of geminal diols and Criegee intermediate