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Abstract Oxygen-containing complex organic molecules are key precursors to biorelevant compounds fundamental for the origins of life. However, the untangling of their interstellar formation mechanisms has just scratched the surface, especially for oxygen-containing cyclic molecules. Here, we present the first laboratory simulation experiments featuring the formation of all three C₂H₄O isomers—ethylene oxide (c–C₂H₄O), acetaldehyde (CH₃CHO), and vinyl alcohol (CH₂CHOH)—in low-temperature model interstellar ices composed of carbon monoxide (CO) and ethanol (C₂H₅OH). Ice mixtures were exposed to galactic cosmic-ray proxies with an irradiation dose equivalent to a cold molecular cloud aged (7 ± 2) × 10⁵yr. These biorelevant species were detected in the gas phase through isomer-selective photoionization reflectron time-of-flight mass spectrometry during temperature-programmed desorption. Isotopic labeling experiments reveal that ethylene oxide is produced from ethanol alone, providing the first experimental evidence to support the hypothesis that ethanol serves as a precursor to the prototype epoxide in interstellar ices. These findings reveal feasible pathways for the formation of all three C₂H₄O isomers in ethanol-rich interstellar ices, offering valuable constraints on astrochemical models for their formation. Our results suggest that ethanol is a critical precursor to C₂H₄O isomers in interstellar environments, representing a critical step toward unraveling the formation mechanisms of oxygen-containing cyclic molecules, aldehydes, and their enol tautomers from alcohols in interstellar ices. 

Abstract Aldehydes are ubiquitous in star-forming regions and carbonaceous chondrites, serving as essential intermediates in metabolic pathways and molecular mass growth processes to vital biomolecules necessary for the origins of life. However, their interstellar formation mechanisms have remained largely elusive. Here, we unveil the formation of lactaldehyde (CH₃CH(OH)CHO) by barrierless recombination of formyl (HĊO) and 1-hydroxyethyl (CH₃ĊHOH) radicals in interstellar ice analogs composed of carbon monoxide (CO) and ethanol (CH₃CH₂OH). Lactaldehyde and its isomers 3-hydroxypropanal (HOCH₂CH₂CHO), ethyl formate (CH₃CH₂OCHO), and 1,3-propenediol (HOCH₂CHCHOH) are identified in the gas phase utilizing isomer-selective photoionization reflectron time-of-flight mass spectrometry and isotopic substitution studies. These findings reveal fundamental formation pathways for complex, biologically relevant aldehydes through non-equilibrium reactions in interstellar environments. Once synthesized, lactaldehyde can act as a key precursor to critical biomolecules such as sugars, sugar acids, and amino acids in deep space. 

This study reveals viable abiotic routes of the three-carbon deoxysugar alcohol 1,2-propanediol (CH₃CH(OH)CH₂OH) and enol 1,2-ethenediol (HOCHCHOH)—a critical intermediate in the formose reaction—in interstellar analog ices. 

This study demonstrates the abiotic formation of biorelevant nitriles—key precursors to amino acids and nucleobases—in interstellar ice analogues of hydrogen cyanide. 

Abstract Enols—tautomers of ketones or aldehydes—are considered key intermediates in the formation of prebiotic sugars and sugar acids. Although laboratory simulation experiments suggest that enols should be ubiquitous in the interstellar medium, the underlying formation mechanisms of enols in interstellar environments are largely elusive. Here, we present the laboratory experiments on the formation of glyoxal (HCOCHO) along with its ynol tautomer acetylenediol (HOCCOH) in interstellar ice analogs composed of carbon monoxide (CO) and water (H₂O) upon exposure to energetic electrons as a proxy for secondary electrons generated from Galactic cosmic rays. Utilizing tunable vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry, glyoxal and acetylenediol were detected in the gas phase during temperature-programmed desorption. Our results reveal the formation pathways of glyoxal via radical–radical recombination of two formyl (HĊO) radicals, and that of acetylenediol via keto-enol-ynol tautomerization. Due to the abundance of carbon monoxide and water in interstellar ices, glyoxal and acetylenediol are suitable candidates for future astronomical searches. Furthermore, the detection of acetylenediol in astrophysically relevant ices advances our understanding for the formation pathways of high-energy tautomers such as enols in deep space. 

Astronomically elusive propen-2-ol and methyl vinyl ether were prepared in irradiated low-temperature acetone ices and detected in the gas phase via photoionization. 

The UV–Vis spectra of H₂CO₃are investigated in a combined experimental and theoretical approach. A sample of solid H₂CO₃, prepared by electron irradiation of water–carbon dioxide ice, shows characteristics of both amorphous and crystalline H₂CO₃in the infrared spectrum. To rationalize the experimentally observed redshift in the UV–Vis spectra between monomer and bulk H₂CO₃, a systematic computational study is devised using time‐dependent density functional theory. H₂CO₃is investigated from the monomer to (H₂CO₃)_nclusters, with n up to 66; in addition regular oligomer arrangements derived from previously proposed ambient‐pressure H₂CO₃crystal structures are also examined. The calculations explain the UV–Vis absorption of solid carbonic acid, which is redshifted by ≈2 eV and ≈5 eV compared to the experimentally observed adiabatic ionization energy of the H₂CO₃monomer. It is highlighted how these shifts emerge due to 1) increasing cluster size, 2) nonplanar arrangements, and 3) noncovalent interactions between H₂CO₃chains and sheets. The study aims to establish spectrum‐to‐structure relationships and serves as computational reference data for astrochemical applications in the absence of experimental laboratory data of H₂CO₃oligomers. 

The tetrahedral P 3 N molecule is prepared via nonequilibrium chemistry at 5 K in ices of phosphine and nitrogen.