Pathways to Oxygen‐Bearing Molecules in the Interstellar Medium and in Planetary Atmospheres: Cyclopropenone (c‐C3H2O) and Propynal (HCCCHO)

We investigated the formation of two C3H2O isomers, i.e., cyclopropenone (c-C3H2O) and propynal (HCCCHO), inbinaryicemixturesof carbonmonoxide(CO)andacetylene(C2H2)at10Kinanultrahighvacuummachineonhighenergy electron irradiation. The chemical evolution of the ice samples was followed online and in situ via a Fourier transform infraredspectrometerand a quadrupolemassspectrometer. The temporalprofilesof the cyclopropenoneand propynal isomers suggest (pseudo-) first-order kinetics. The cyclic structure (c-C3H2O) is formed via an addition of triplet carbon monoxide to ground-state acetylene (or vice versa); propynal (HCCCHO) can be synthesized from a carbonmonoxideYacetylenecomplexviaa[HCO ... CCH] radical pairinsidethematrixcage.Theselaboratorystudies showedforthefirsttimethatbothC3H2Oisomerscanbeformedinlow-temperatureicesvianonequilibriumchemistry initiated by energetic electrons as formed in the track of Galactic cosmic ray particles penetrating interstellar icy grains in cold molecular clouds. Our results can explain the hitherto unresolved gas phase abundances of cyclopropenone in star-formingregions via sublimation of c-C3H2O as formed on icy grains in the cold molecularcloud stage. Implications for the heterogeneous oxygen chemistry of Titan and icy terrestrial planets and satellites suggest that the production of oxygen-bearing molecules such as C3H2O may dominate on aerosol particles compared to pure gas phase chemistry. Subject headingg astrobiology — astrochemistry — ISM: molecules — planets and satellites: individual (Titan) Online material: color figures