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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. 

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. 

Abstract Owing to the unique conditions in cold molecular clouds, enols—the thermodynamically less stable tautomers of aldehydes and ketones—do not undergo tautomerization to their more stable tautomers in the gas phase because they cannot overcome tautomerization barriers at the low temperatures. Laboratory studies of interstellar analog ices have demonstrated the formation of several keto–enol tautomer pairs in astrochemically relevant ice mixtures over the last years. However, so far only one of them, acetaldehyde−vinyl alcohol, has been detected in deep space. Due to their reactivity with electrophiles, enols can play a crucial role in our understanding of the molecular complexity in the interstellar medium and in comets and meteorites. To study the enolization of aldehydes in interstellar ices by interaction with galactic cosmic rays (GCRs), we irradiated acetaldehyde ices with energetic electrons as proxies of secondary electrons generated in the track of GCRs while penetrating interstellar ices. The results indicate that GCRs can induce enolization of acetaldehyde and that intra‐ as well as intermolecular processes are relevant. Therefore, enols should be ubiquitous in the interstellar medium and could be searched for using radio telescopes such as ALMA. Once enols are detected and abundances are established, they can serve as tracers for the non‐equilibrium chemistry in interstellar ices thus eventually constraining fundamental reaction mechanisms deep inside interstellar ices. 

Abstract The hitherto elusive monobridged Ge(μ‐H)GeH (X¹A′) molecule was prepared in the gas phase by bimolecular reaction of atomic germanium with germane (GeH₄). Electronic structure calculations revealed that this reaction commenced on the triplet surface with the formation of a van der Waals complex, followed by insertion of germanium into a germanium‐hydrogen bond over a submerged barrier to form the triplet digermanylidene intermediate (HGeGeH₃); the latter underwent intersystem crossing from the triplet to the singlet surface. On the singlet surface, HGeGeH₃predominantly isomerized through two successive hydrogen shifts prior to unimolecular decomposition to Ge(μ‐H)GeH isomer, which is in equilibrium with the vinylidene‐type (H₂GeGe) and dibridged (Ge(μ‐H₂)Ge) isomers. This reaction leads to the formation of cyclic dinuclear germanium molecules, which do not exist on the isovalent C₂H₂surface, thus deepening our understanding of the role of nonadiabatic reaction dynamics in preparing nonclassical, hydrogen‐bridged isomers carrying main group XIV elements. 

Abstract Glycinal (HCOCH₂NH₂) and acetamide (CH₃CONH₂) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic rays. Glycinal and acetamide are accessed via barrierless radical‐radical reactions of vinoxy (⋅CH₂CHO) and acetyl (⋅C(O)CH₃), and then undergo keto‐enol tautomerization. Exploiting tunable photoionization reflectron time‐of‐flight mass spectroscopy and photoionization efficiency (PIE) curves, these results demonstrate fundamental reaction pathways for the formation of complex organics through non‐equilibrium ice reactions in cold molecular cloud environments. These molecules demonstrate an unconventional starting point for abiotic synthesis of organics relevant to contemporary biomolecules like polypeptides and cell membranes in deep space. 

Abstract The previously unknown silylgermylidyne radical (H₃SiGe; X²A′′) was prepared via the bimolecular gas phase reaction of ground state silylidyne radicals (SiH; X²Π) with germane (GeH₄; X¹A₁) under single collision conditions in crossed molecular beams experiments. This reaction begins with the formation of a van der Waals complex followed by insertion of silylidyne into a germanium‐hydrogen bond forming the germylsilyl radical (H₃GeSiH₂). A hydrogen migration isomerizes this intermediate to the silylgermyl radical (H₂GeSiH₃), which undergoes a hydrogen shift to an exotic, hydrogen‐bridged germylidynesilane intermediate (H₃Si(μ‐H)GeH); this species emits molecular hydrogen forming the silylgermylidyne radical (H₃SiGe). Our study offers a remarkable glance at the complex reaction dynamics and inherent isomerization processes of the silicon‐germanium system, which are quite distinct from those of the isovalent hydrocarbon system (ethyl radical; C₂H₅) eventually affording detailed insights into an exotic chemistry and intriguing chemical bonding of silicon‐germanium species at the microscopic level exploiting crossed molecular beams. 

Abstract The chemical dynamics of the elementary reaction of ground state atomic silicon (Si;³P) with germane (GeH₄; X¹A₁) were unraveled in the gas phase under single collision condition at a collision energy of 11.8±0.3 kJ mol⁻¹exploiting the crossed molecular beams technique contemplated with electronic structure calculations. The reaction follows indirect scattering dynamics and is initiated through an initial barrierless insertion of the silicon atom into one of the four chemically equivalent germanium‐hydrogen bonds forming a triplet collision complex (HSiGeH₃;³i1). This intermediate underwent facile intersystem crossing (ISC) to the singlet surface (HSiGeH₃;¹i1). The latter isomerized via at least three hydrogen atom migrations involving exotic, hydrogen bridged reaction intermediates eventually leading to the H₃SiGeH isomeri5. This intermediate could undergo unimolecular decomposition yielding the dibridged butterfly‐structured isomer¹p1(Si(μ‐H₂)Ge) plus molecular hydrogen through a tight exit transition state. Alternatively, up to two subsequent hydrogen shifts toi6andi7, followed by fragmentation of each of these intermediates, could also form¹p1(Si(μ‐H₂)Ge) along with molecular hydrogen. The overall non‐adiabatic reaction dynamics provide evidence on the existence of exotic dinuclear hydrides of main group XIV elements, whose carbon analog structures do not exist. 

Abstract We report the formation of the cyclic methylphosphonic acid trimer [c‐(CH₃PO₂)₃] through condensation reactions during thermal processing of low‐temperature methylphosphonic acid samples exploiting photoionization reflectron time‐of‐flight mass spectrometry (PI−ReTOF−MS) along with electronic structure calculations. Cyclic methylphosphonic acid trimers are formed in the solid state and detected together with its protonated species in the gas phase upon single photon ionization. Our studies provide an understanding of the preparation of phosphorus‐bearing potentially prebiotic molecules and the fundamental knowledge of low‐temperature phosphorus chemistry in extraterrestrial environments. 

Abstract Ices of acetylene (C₂H₂) and ammonia (NH₃) were irradiated with energetic electrons to simulate interstellar ices processed by galactic cosmic rays in order to investigate the formation of C₂H₃N isomers. Supported by quantum chemical calculations, experiments detected product molecules as they sublime from the ices using photoionization reflectron time‐of‐flight mass spectrometry (PI‐ReTOF‐MS). Isotopically‐labeled ices confirmed the C₂H₃N assignments while photon energies of 8.81 eV, 9.80 eV, and 10.49 eV were utilized to discriminate isomers based on their known ionization energies. Results indicate the formation of ethynamine (HCCNH₂) and 2H‐azirine (c‐H₂CCHN) in the irradiated C₂H₂:NH₃ices, and the energetics of their formation mechanisms are discussed. These findings suggest that these two isomers can form in interstellar ices and, upon sublimation during the hot core phase, could be detected using radio astronomy.