This work reveals via a combined experimental, computational, and astrochemical modeling study that racemic propylene oxide (c-C₃H₆O)—the first chiral molecule detected outside Earth toward the high-mass star-forming region Sagittarius B2(N)—can be synthesized by non-equilibrium reactions initiated by the effects of secondary electrons generated in the track of cosmic rays interacting with ice-coated interstellar grains through excited-state and spin-forbidden reaction pathways operating within low-temperature interstellar ices at 10 K. Our findings confront traditional hypotheses that thermal chemistries followed by processing of interstellar grains dictate the formation of complex organic molecules (COMs) in molecular clouds. Instead, we reveal a hitherto poorly quantified reaction class involving excited-state and spin-forbidden chemistry leading to racemic mixtures of COMs inside interstellar ices prior to their sublimation in star-forming regions. This fundamental production mechanism is of essential consequence in aiding our understanding of the origin and evolution of chiral molecules in the universe.

The underlying formation mechanisms of complex organic molecules (COMs)—in particular, structural isomers—in the interstellar medium (ISM) are largely elusive. Here, we report new experimental findings on the role of methanol (CH₃OH) and methane (CH₄) ices in the synthesis of two C₂H₆O isomers upon interaction with ionizing radiation: ethanol (CH₃CH₂OH) and dimethyl ether (CH₃OCH₃). The present study reproduces the interstellar abundance ratios of both species with ethanol to dimethyl ether branching ratios of (2.33 ± 0.14):1 suggesting that methanol and methane represents the key precursor to both isomers within interstellar ices. Exploiting isotopic labeling combined with reflectron time-of-flight mass spectrometry (Re-TOF-MS) after isomer selective vacuum ultra-violet (VUV) photoionization of the neutral molecules, we also determine the formation mechanisms of both isomers via radical–radical recombination versus carbene (CH₂) insertion with the former pathway being predominant. Formation routes to higher molecular weight reaction products such as ethylene glycol (HOCH₂CH₂OH), dimethyl peroxide (CH₃OOCH₃), and methoxymethanol (CH₃OCH₂OH) are discussed briefly as well.

The structural isomers ethanol (CH₃CH₂OH) and dimethyl ether (CH₃OCH₃) were detected in several low-, intermediate-, and high-mass star-forming regions, including Sgr B2, Orion, and W33A, with the relative abundance ratios of ethanol/dimethyl ether varying from about 0.03 to 3.4. Until now, no experimental data regarding the formation mechanisms and branching ratios of these two species in laboratory simulation experiments could be provided. Here, we exploit tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) to detect and analyze the production of complex organic molecules (COMs) resulting from the exposure of water/methane (H₂O/CH₄) ices to energetic electrons. The main goal is to understand the formation mechanisms in star-forming regions of two C₂H₆O isomers: ethanol (CH₃CH₂OH) and dimethyl ether (CH₃OCH₃). The results show that the experimental branching ratios favor the synthesis of ethanol versus dimethyl ether (31 ± 11:1). This finding diverges from the abundances observed toward most star-forming regions, suggesting that production routes on interstellar grains to form dimethyl ether might be missing; alternatively, ethanol can be overproduced in the present simulation experiments, such as via radical–radical recombination pathways involving ethyl and hydroxyl radicals. Finally, the PI-ReTOF-MS data suggest the formation of methylacetylene (C₃H₄), ketene (CH₂CO), propene (C₃H₆), vinyl alcohol (CH₂CHOH), acetaldehyde (CH₃CHO), and methyl hydroperoxide (CH₃OOH), in addition to ethane (C₂H₆), methanol (CH₃OH), and CO₂ detected from infrared spectroscopy. The yield of all the confirmed species is also determined.

The –CH–NH₂ moiety represents the fundamental building block of all proteinogenic amino acids, with the cyclic amino acid proline being a special case (–CH–NH– in proline). Exploiting a chemical retrosynthesis, we reveal that methylamine (CH₃NH₂) and/or ethylamine (CH₃CH₂NH₂) are essential precursors in the formation of each proteinogenic amino acid. In the present study we elucidate the abiotic formation of methylamine and ethylamine from ammonia (NH₃) and methane (CH₄) ices exposed to secondary electrons generated by energetic cosmic radiation in cometary and interstellar model ices. Our experiments show that methylamine and ethylamine are crucial reaction products in irradiated ices composed of ammonia and methane. Using isotopic substitution studies we further obtain valuable information on the specific reaction pathways toward methylamine. The very recent identification of methylamine and ethylamine together with glycine in the coma of 67P/Churyumov–Gerasimenko underlines their potential to the extraterrestrial formation of amino acids.

Phosphorus signifies an essential element in molecular biology, yet given the limited solubility of phosphates on early Earth, alternative sources like meteoritic phosphides have been proposed to incorporate phosphorus into biomolecules under prebiotic terrestrial conditions. Here, we report on a previously overlooked source of prebiotic phosphorus from interstellar phosphine (PH₃) that produces key phosphorus oxoacids—phosphoric acid (H₃PO₄), phosphonic acid (H₃PO₃), and pyrophosphoric acid (H₄P₂O₇)—in interstellar analog ices exposed to ionizing radiation at temperatures as low as 5 K. Since the processed material of molecular clouds eventually enters circumstellar disks and is partially incorporated into planetesimals like proto Earth, an understanding of the facile synthesis of oxoacids is essential to untangle the origin of water-soluble prebiotic phosphorus compounds and how they might have been incorporated into organisms not only on Earth, but potentially in our universe as well.

The formation of isomers of C₂H₂O—ketene (H₂CCO), ethynol (HCCOH), and oxirene (c-CHCHO)—was investigated in interstellar ice analogs composed of carbon monoxide and water. Using tunable photoionization time-of-flight mass spectrometry to selectively ionize the isomer of interest, ketene and ethynol were detected as reaction products, but oxirene remains elusive. These findings demonstrate that organic compounds that are precursors to complex organic molecules can form without an organic source of carbon. Furthermore, we report the first plausible detection of ethynol in astrophysically relevant ices. These investigations were supported by theoretical calculations describing reaction energies, pathways, ionization energies, and harmonic frequencies.