The astrochemical evolutionary traits of phospholipid membrane homochirality

Compartmentalization is crucial for the evolution of life. Present-day phospholipid membranes exhibit a high level of complexity and species-dependent homochirality, the so-called lipid divide. It is possible that less stable, yet more dynamic systems, promoting out-of-equilibrium environments, facilitated the evolution of life at its early stages. The composition of the preceding primitive membranes and the evolutionary route towards complexity and homochirality remain unexplained. Organics-rich carbonaceous chondrites are evidence of the ample diversity of interstellar chemistry, which may have enriched the prebiotic milieu on early Earth. This Review evaluates the detections of simple amphiphiles - likely ancestors of membrane phospholipids - in extraterrestrial samples and analogues, along with potential pathways to form primitive compartments on primeval Earth. The chiroptical properties of the chiral backbones of phospholipids provide a guide for future investigations into the origins of phospholipid membrane homochirality. We highlight a plausible common pathway towards homochirality of lipids, amino acids, and sugars starting from enantioenriched monomers. Finally, given their high recalcitrance and resistance to degradation, lipids are among the best candidate biomarkers in exobiology.

AQUILA: A laboratory facility for the irradiation of astrochemical ice analogs by keV ions

The detection of various molecular species, including complex organic molecules relevant to biochemical and geochemical processes, in astronomical settings, such as the interstellar medium or the outer solar system, has led to the increased need for a better understanding of the chemistry occurring in these cold regions of space. In this context, the chemistry of ices prepared and processed at cryogenic temperatures has proven to be of particular interest due to the fact that many interstellar molecules are believed to originate within the icy mantles adsorbed on nano- and micro-scale dust particles. The chemistry leading to the formation of such molecules may be initiated by ionizing radiation in the form of galactic cosmic rays or stellar winds, and thus, there has been an increased interest in commissioning experimental setups capable of simulating and better characterizing this solid-phase radiation astrochemistry. In this article, we describe a new facility called AQUILA (Atomki-Queen's University Ice Laboratory for Astrochemistry), which has been purposefully designed to study the chemical evolution of ices analogous to those that may be found in the dense interstellar medium or the outer solar system as a result of their exposure to keV ion beams. The results of some ion irradiation studies of CH3OH ice at 20 K are discussed to exemplify the experimental capabilities of the AQUILA as well as to highlight its complementary nature to another laboratory astrochemistry setup at our institute.

An investigation into transition states of cyclic tetra-atomic silicon and germanium interstellar dust compounds: SixC4-x, GexC4-x, and GexSi4-x (x ∈ {1,2,3})

Presented in this work is a thorough determination of the transition states between the different isomers of cyclic tetra-atomic silicon carbide, germanium carbide, and germanium silicide clusters. Through use of density functional theory (B3LYP-D3BJ, M06-2X, ωB97X-D4, and B2GP-PLYP) in conjunction with the aug-cc-pVTZ basis set, transition state structures and their barrier heights are determined for the interconversions between the various isomers for the family of tetra-atomic SiC, GeC, and GeSi compounds. SiC dust grains are known to be prevalent in interstellar dust, and among this group, so far only diamond-shaped (d-)SiC3 has been detected in the interstellar medium (ISM). Determining which other structures might be detectable not only depends on their intrinsic spectroscopic features, but whether or not they are likely to exist as isomers in interstellar environments. By examining the energy barrier heights for transitions between isomers, we determined that many of these structures are unlikely to exhibit interconversion in the ISM, outside of hotter circumstellar environments. Although Boltzmann population ratios at approximate circumstellar temperatures suggest the presence of higher energy minima, it is likely that once interconversion happens, as molecules travel away from a star and cool, they will get kinetically trapped in the potential energy well they inhabit, making how the ratios freeze out dependent on the time and pathways the molecules take to cool down. As such, many of these higher energy minima may still be good candidates for detection including (rhomboidal) r-SiC3, r-GeC3, r-GeSi3, (trapezoidal) t-Si2C2, r-Ge2C2, and d-Si3C.

Condensed Matter Systems Exposed to Radiation: Multiscale Theory, Simulations, and Experiment

This roadmap reviews the new, highly interdisciplinary research field studying the behavior of condensed matter systems exposed to radiation. The Review highlights several recent advances in the field and provides a roadmap for the development of the field over the next decade. Condensed matter systems exposed to radiation can be inorganic, organic, or biological, finite or infinite, composed of different molecular species or materials, exist in different phases, and operate under different thermodynamic conditions. Many of the key phenomena related to the behavior of irradiated systems are very similar and can be understood based on the same fundamental theoretical principles and computational approaches. The multiscale nature of such phenomena requires the quantitative description of the radiation-induced effects occurring at different spatial and temporal scales, ranging from the atomic to the macroscopic, and the interlinks between such descriptions. The multiscale nature of the effects and the similarity of their manifestation in systems of different origins necessarily bring together different disciplines, such as physics, chemistry, biology, materials science, nanoscience, and biomedical research, demonstrating the numerous interlinks and commonalities between them. This research field is highly relevant to many novel and emerging technologies and medical applications.

Infrared Spectral Signatures of Nucleobases in Interstellar Ices I: Purines

The purine nucleobases adenine and guanine are complex organic molecules that are essential for life. Despite their ubiquitous presence on Earth, purines have yet to be detected in observations of astronomical environments. This work therefore proposes to study the infrared spectra of purines linked to terrestrial biochemical processes under conditions analogous to those found in the interstellar medium. The infrared spectra of adenine and guanine, both in neat form and embedded within an ice made of H2O:NH3:CH4:CO:CH3OH (10:1:1:1:1), were analysed with the aim of determining which bands attributable to adenine and/or guanine can be observed in the infrared spectrum of an astrophysical ice analogue rich in other volatile species known to be abundant in dense molecular clouds. The spectrum of adenine and guanine mixed together was also analysed. This study has identified three purine nucleobase infrared absorption bands that do not overlap with bands attributable to the volatiles that are ubiquitous in the dense interstellar medium. Therefore, these three bands, which are located at 1255, 940, and 878 cm-1, are proposed as an infrared spectral signature for adenine, guanine, or a mixture of these molecules in astrophysical ices. All three bands have integrated molar absorptivity values (ψ) greater than 4 km mol-1, meaning that they should be readily observable in astronomical targets. Therefore, if these three bands were to be observed together in the same target, then it is possible to propose the presence of a purine molecule (i.e., adenine or guanine) there.

Acid Enriched with Methanol: Formation of a Prebiotic Cluster in the Interstellar Medium

Organic molecules are a potential source of prebiotic chemistry in the interstellar medium (ISM). Methanol (MetOH) is a very important source of more complex molecules. H 3 O + (aq) and Cl - (aq) are fundamental to living organisms and can be generated in the ISM from the dissociation of HCl with just four water molecules, yielding the (H 3 O) + (H 2 O) 3 Cl - ion-pair. Here, a detailed mechanism, based on density functional theory (DFT) and ab-initio (2 nd order Mfller-Plesset perturbation theory, MP2) calculations, is suggested for the substitution reactions of these water molecules by MetOH. The time required for formation of an appreciable amount of the product ((H 3 O) + (MetOH) 3 Cl - ) can be only few years. Such reaction can take place in Sagittarius B2, where HCl, H 2 O and MetOH have already been identified and it can be an important source for the formation of more complex prebiotic structures.

Computational studies on the possible formation of glycine via open shell gas-phase chemistry in the interstellar medium

Glycine is the simplest proteinogenic amino acid. It has significant astrobiological implications owing to the ongoing investigation for its detection in the interstellar medium (ISM). Hence, a suitable mechanistic elucidation for its formation in the ISM is of current research interest. In the present work, by employing electronic structure calculations [UCCSD(T) and density functional theory (DFT)], various plausible chemical pathways in the gas phase have been examined for the formation of glycine (whose existence has been indirectly proposed in the ISM) and other simple amino acids (yet to be detected in the ISM) from some simpler molecules present in the ISM. This work suggests that step 1: HO-CO (radical) + CH₂NH → NHCH₂COOH (radical) and step 2a: NHCH₂COOH (radical) + H₂ → glycine + H (radical) have very small barriers of 0.14 kcal mol^-1 and ∼3 kcal mol^-1, respectively (easily surmountable at a temperature of ∼50 K under putative interstellar conditions). Hence this should likely be feasible in interstellar gas-phase chemistry. Therefore, HO-CO (radical), CH₂NH, and H₂ could be the possible precursors for the formation of glycine (subject to the presence of the HO-CO radical). The energetic information related to the interstellar reactions, and how this work takes the putative interstellar conditions into account are presented. This paper also highlights how a reaction found to be unsuitable for interstellar molecular evolution via surface chemistry could nonetheless occur via gas-phase chemistry. Based on our results, this work also recommends detecting three new open-shell molecules, HO-CO radical, NHCH₂COOH radical, and NH₂CHCOOH radical, in the ISM.

Tracing the Primordial Chemical Life of Glycine: A Review from Quantum Chemical Simulations

Glycine (Gly), NH2CH2COOH, is the simplest amino acid. Although it has not been directly detected in the interstellar gas-phase medium, it has been identified in comets and meteorites, and its synthesis in these environments has been simulated in terrestrial laboratory experiments. Likewise, condensation of Gly to form peptides in scenarios resembling those present in a primordial Earth has been demonstrated experimentally. Thus, Gly is a paradigmatic system for biomolecular building blocks to investigate how they can be synthesized in astrophysical environments, transported and delivered by fragments of asteroids (meteorites, once they land on Earth) and comets (interplanetary dust particles that land on Earth) to the primitive Earth, and there react to form biopolymers as a step towards the emergence of life. Quantum chemical investigations addressing these Gly-related events have been performed, providing fundamental atomic-scale information and quantitative energetic data. However, they are spread in the literature and difficult to harmonize in a consistent way due to different computational chemistry methodologies and model systems. This review aims to collect the work done so far to characterize, at a quantum mechanical level, the chemical life of Gly, i.e., from its synthesis in the interstellar medium up to its polymerization on Earth.

Water formation on interstellar silicates: the role of Fe2+/H2 interactions in the O + H2 → H2O reaction

Water formation by reaction of H2 and O on silicate surfaces as a first step towards the generation of interstellar ice mantles is possible thanks to the activation of H2 inferred by Fe2+ ions and quantum tunnelling effects.

An Innovative Approach for the Generation of Species of the Interstellar Medium

The large amount of unstable species in the realm of interstellar chemistry drives an urgent need to develop efficient methods for the in situ generations of molecules that enable their spectroscopic characterizations. Such laboratory experiments are fundamental to decode the molecular universe by matching the interstellar and terrestrial spectra. We propose an approach based on laser ablation of nonvolatile solid organic precursors. The generated chemical species are cooled in a supersonic expansion and probed by high‐resolution microwave spectroscopy. We present a proof of concept through a simultaneous formation of interstellar compounds and the first generation of aminocyanoacetylene using diaminomaleonitrile as a prototypical precursor. With this micro‐laboratory, we open the door to generation of unsuspected species using precursors not typically accessible to traditional techniques such as electric discharge and pyrolysis.

"Smart Decomposition" of Cyclic Alanine-Alanine Dipeptide by VUV Radiation: A Seed for the Synthesis of Biologically Relevant Species

A combined experimental and theoretical study shows how the interaction of VUV radiation with cyclo-(alanine-alanine), one of the 2,5-diketopiperazines (DKPs), produces reactive oxazolidinone intermediates. The theoretical simulations reveal that the interaction of these intermediates with other neutral and charged fragments, released in the molecular decomposition, leads either to the reconstruction of the cyclic dipeptide or to the formation of longer linear peptide chains. These results may explain how DKPs could have, on one hand, survived hostile chemical environments and, on the other, provided the seed for amino acid polymerization. Shedding light on the mechanisms of production of such prebiotic building blocks is of paramount importance to understanding the abiotic synthesis of relevant biologically active compounds.

Rotational and Vibrational Signatures of Astrophyscially relevant Gas-Phase Stereo-isomeric Species of Proteinogenic Amino acid Leucine

The search for life-supporting molecules in outer space is an ever-growing endeavour. Towards this, the computational chemistry supporting the astronomical spectroscopic observations is becoming a valuable tool to unravel the complex chemical network in interstellar medium (ISM). In the present work, quantum-mechanical computations, accounting for anharmonic effects, are performed to obtain the rotational and vibrational line-data for the gas-phase conformers of proteinogenic amino acid Leucine and its isomeric species predicted to be involved in its stereoinversion under the extreme environment of ISM. These species exhibit diverse chemistry including branched skeleton and zwitterionic ammonium ylides. A few of the species have significantly high dipole moment, which can act as tracer for the conformers of Leucine having low dipole moment. Besides this, the species, which are terrestrially less stable, can be of significant importance to the astronomers. Notably, the spectral database generated in this work can assist in the detection of proteinogenic Leucine and its isomeric species in different regions of ISM.

Pathways for the Formation of Formamide, a Prebiotic Biomonomer: Metal-Ions in Interstellar Gas-Phase Chemistry

The chemistry occurring in the interstellar medium (ISM) is an active area of contemporary research. New aspects of interstellar chemistry are getting unraveled regularly. In this context, the role of metal-ions in the chemistry occurring in the ISM is not well-studied so far. Herein, we highlight the role of metal-ions in interstellar chemistry. For this purpose, we choose the problem of gas-phase formamide formation in interstellar molecular clouds. Formamide is a key biomonomer and contains the simplest peptide [-(C═O)-NH-] linkage. With its two electronegative atoms ("O" and "N"), it provides an excellent platform to probe the role of the metal-ions. The metal-ions chosen are Na⁺, K⁺, Al⁺, Mg⁺, and Mg²⁺-all of them present in the ISM. The metal-ions are studied in three different forms as bare positively charged ions, as hydrated metal-ions co-ordinated with a molecule of water, and when the metal-ions are part of a neutral covalent molecule. With the aid of electronic structure calculations [CCSD(T) and DFT methods], we study different gas-phase pathways which result in the generation of interstellar formamide. Throughout our study, we find that metal-ions lower the barriers (with Mg⁺, Mg⁺⁺, and Al⁺ offering maximal stabilization of the transition states) and facilitate the reactions. The chemical factors influencing the reactions, how we consider the putative conditions in the ISM, the astrochemical implications of this study, and its connection with terrestrial prebiotic chemistry and refractory astrochemistry are subsequently presented. Based on our results, we also recommend the detection of two new closed-shell molecules, NH₂CH₂OH (aminomethanol) and CH₂NH₂⁺ (iminium ion), and two open-shell molecules, CONH₂ (carbamyl radical) and HCONH (an isomer of carbamyl radical), in the ISM.

Complex Organic Matter Synthesis on Siloxyl Radicals in the Presence of CO

Heterogeneous phase astrochemistry plays an important role in the synthesis of complex organic matter (COM) as found on comets and rocky body surfaces like asteroids, planetoids, moons and planets. The proposed catalytic model is based on two assumptions: (a) siliceous rocks in both crystalline or amorphous states show surface-exposed defective centers such as siloxyl (Si-O•) radicals; (b) the second phase is represented by gas phase CO molecules, an abundant C₁ building block found in space. By means of quantum chemistry; (DFT, PW6B95/def2-TZVPP); the surface of a siliceous rock in presence of CO is modeled by a simple POSS (polyhedral silsesquioxane) where a siloxyl (Si-O•) radical is present. Four CO molecules have been consecutively added to the Si-O• radical and to the nascent polymeric CO (pCO) chain. The first CO insertion shows no activation free energy with ΔG_200K = −21.7 kcal/mol forming the SiO-CO• radical. The second and third CO insertions show ΔG200K‡ ≤ 10.5 kcal/mol. Ring closure of the SiO-CO-CO• (oxalic anhydride) moiety as well as of the SiO-CO-CO-CO• system (di-cheto form of oxetane) are thermodynamically disfavored. The last CO insertion shows no free energy of activation resulting in the stable five member pCO ring, precursor to 1,4-epoxy-1,2,3-butanone. Hydrogenation reactions of the pCO have been considered on the SiO oxygen or on the carbons and oxygens of the pCO chains. The formation of the reactive aldehyde SiO-CHO on the siliceous surface is possible. In principle, the complete hydrogenation of the (CO)₁₋₄ series results in the formation of methanol and polyols. Furthermore, all the SiO-pCO intermediates and the lactone 1,4-epoxy-1,2,3-butanone product in its radical form can be important building blocks in further polymerization reactions and/or open ring reactions with H (aldehydes, polyols) or CN (chetonitriles), resulting in highly reactive multi-functional compounds contributing to COM synthesis.

Computational Surface Modelling of Ices and Minerals of Interstellar Interest—Insights and Perspectives

The universe is molecularly rich, comprising from the simplest molecule (H2) to complex organic molecules (e.g., CH3CHO and NH2CHO), some of which of biological relevance (e.g., amino acids). This chemical richness is intimately linked to the different physical phases forming Solar-like planetary systems, in which at each phase, molecules of increasing complexity form. Interestingly, synthesis of some of these compounds only takes place in the presence of interstellar (IS) grains, i.e., solid-state sub-micron sized particles consisting of naked dust of silicates or carbonaceous materials that can be covered by water-dominated ice mantles. Surfaces of IS grains exhibit particular characteristics that allow the occurrence of pivotal chemical reactions, such as the presence of binding/catalytic sites and the capability to dissipate energy excesses through the grain phonons. The present know-how on the physicochemical features of IS grains has been obtained by the fruitful synergy of astronomical observational with astrochemical modelling and laboratory experiments. However, current limitations of these disciplines prevent us from having a full understanding of the IS grain surface chemistry as they cannot provide fundamental atomic-scale of grain surface elementary steps (i.e., adsorption, diffusion, reaction and desorption). This essential information can be obtained by means of simulations based on computational chemistry methods. One capability of these simulations deals with the construction of atom-based structural models mimicking the surfaces of IS grains, the very first step to investigate on the grain surface chemistry. This perspective aims to present the current state-of-the-art methods, techniques and strategies available in computational chemistry to model (i.e., construct and simulate) surfaces present in IS grains. Although we focus on water ice mantles and olivinic silicates as IS test case materials to exemplify the modelling procedures, a final discussion on the applicability of these approaches to simulate surfaces of other cosmic grain materials (e.g., cometary and meteoritic) is given.

Theoretical Investigation of a Vital Step in the Gas-Phase Formation of Interstellar Ammonia NH2+ + H2 → NH3+ + H

A crucial step in the gas-phase formation of ammonia in the interstellar medium (ISM) is the reaction of NH₂⁺ with molecular hydrogen. Understanding the electronic structure of the participating species in this reaction and the evaluation of the rate coefficients at interstellar temperatures are, therefore, critical to gain new insights into the mechanisms of formation of interstellar ammonia. We present here the first theoretical results of the rate coefficients of this reaction as a function of temperatures relevant to the ISM, computed using transition-state theory. The results are in reasonable agreement with recent experimental data. This exothermic reaction features a tiny barrier which is primarily a consequence of zero-point energy corrections. The results demonstrate that quantum mechanical tunneling and core-electron correlations play significant roles in determining the rate of the reaction. The noteworthy failure of popular density functionals to describe this reaction is also highlighted.

The carbon and oxygen K-edge NEXAFS spectra of CO+

We present and analyze high resolution near edge X-ray absorption fine structure (NEXAFS) spectra of CO⁺ at the carbon and oxygen K-edges.

The challenging playground of astrochemistry: an integrated rotational spectroscopy - quantum chemistry strategy

While it is now well demonstrated that the interstellar medium (ISM) is characterized by a diverse and complex chemistry, a significant number of features in radioastronomical spectra are still unassigned and call for new laboratory efforts, which are increasingly based on integrated experimental and computational strategies. In parallel, the identification of an increasing number of molecules containing more than five atoms and at least one carbon atom (the so-called "interstellar" complex organic molecules), which can play a relevant role in the chemistry of life, raises the additional issue of how these species can be produced in the typical harsh conditions of the ISM. On these grounds, this perspective aims to present an integrated rotational spectroscopy - quantum chemistry approach for supporting radioastronomical observations and a computational strategy for contributing to the elucidation of chemical reactivity in the interstellar space.

Role of Mineral Surfaces in Prebiotic Chemical Evolution. In Silico Quantum Mechanical Studies

There is a consensus that the interaction of organic molecules with the surfaces of naturally-occurring minerals might have played a crucial role in chemical evolution and complexification in a prebiotic era. The hurdle of an overly diluted primordial soup occurring in the free ocean may have been overcome by the adsorption and concentration of relevant molecules on the surface of abundant minerals at the sea shore. Specific organic⁻mineral interactions could, at the same time, organize adsorbed molecules in well-defined orientations and activate them toward chemical reactions, bringing to an increase in chemical complexity. As experimental approaches cannot easily provide details at atomic resolution, the role of in silico computer simulations may fill that gap by providing structures and reactive energy profiles at the organic⁻mineral interface regions. Accordingly, numerous computational studies devoted to prebiotic chemical evolution induced by organic⁻mineral interactions have been proposed. The present article aims at reviewing recent in silico works, mainly focusing on prebiotic processes occurring on the mineral surfaces of clays, iron sulfides, titanium dioxide, and silica and silicates simulated through quantum mechanical methods based on the density functional theory (DFT). The DFT is the most accurate way in which chemists may address the behavior of the molecular world through large models mimicking chemical complexity. A perspective on possible future scenarios of research using in silico techniques is finally proposed.

A cryogenic cylindrical ion trap velocity map imaging spectrometer

A cryogenic cylindrical ion trap velocity map imaging spectrometer has been developed to study photodissociation spectroscopy and dynamics of gaseous molecular ions and ionic complexes. A cylindrical ion trap made of oxygen-free copper is cryogenically cooled down to ∼7 K by using a closed cycle helium refrigerator and is coupled to a velocity map imaging (VMI) spectrometer. The cold trap is used to cool down the internal temperature of mass selected ions and to reduce the velocity spread of ions after extraction from the trap. For CO₂ ⁺ ions, a rotational temperature of ∼12 K is estimated from the recorded [1 + 1] two-photon dissociation spectrum, and populations in spin-orbit excited X²Π_g,1/2 and vibrationally excited states of CO₂ ⁺ are found to be non-detectable, indicating an efficient internal cooling of the trapped ions. Based on the time-of-flight peak profile and the image of N₃ ⁺, the velocity spread of the ions extracted from the trap, both radially and axially, is interpreted as approximately ±25 m/s. An experimental image of fragmented Ar⁺ from 307 nm photodissociation of Ar₂ ⁺ shows that, benefitting from the well-confined velocity spread of the cold Ar₂ ⁺ ions, a VMI resolution of Δv/v ∼ 2.2% has been obtained. The current instrument resolution is mainly limited by the residual radial speed spread of the parent ions after extraction from the trap.

Gas-Phase Stereoinversion in Aspartic Acid: Reaction Pathways, Computational Spectroscopic Analysis, and Its Astrophysical Relevance

Noncatalytic reaction pathways for the gas-phase stereoinversion in aspartic acid are mapped employing a global reaction route mapping strategy using quantum mechanical computations. The species including the transition states (TSs) traced along the stereoinversion pathways are characterized using rotational and vibrational computational spectroscopic analysis while accounting for the vibrational corrections to rotational constants and anharmonic effects. Notably, the TS structures traced along the stereochemical pathways resemble the achiral ammonium ylide and imine intermediates as observed in the Strecker synthesis of chiral amino acids. A few of the probable stereoinversion pathways proposed proceed through the proton or hydrogen atom transfer. The feasibility of the pathways under conditions akin to interstellar medium (ISM) is further discussed in terms of natural bond orbital analysis. The stereoinversion pathways proposed in this work may proceed via photoirradiation in the ISM, which though can be revealed by exploring the excited-state potential energy surface. In this context, the spectroscopic data generated in this work can provide valuable assistance toward the astrophysical detection of chiral molecules in outer space.

Astrochemistry: overview and challenges

This paper provides a brief overview of the journey of molecules through the Cosmos, from local diffuse interstellar clouds and PDRs to distant galaxies, and from cold dark clouds to hot star-forming cores, protoplanetary disks, planetesimals and exoplanets. Recent developments in each area are sketched and the importance of connecting astronomy with chemistry and other disciplines is emphasized. Fourteen challenges for the field of Astrochemistry in the coming decades are formulated.

IGLIAS: A new experimental set-up for low temperature irradiation studies at large irradiation facilities

We designed and built a mobile experimental set-up for studying the interaction of ion beams with solid samples in a wide temperature range from 9 to 300 K. It is either possible to mount up to three samples prepared ex situ or to prepare samples by condensation of molecules from gases or vapours onto IR or Visible-ultraviolet (Vis-UV) transparent windows. The physico-chemical evolution during irradiation can be followed in situ with different analysis techniques including Fourier transform infrared spectroscopy, Vis-UV, and quadrupole mass spectrometry.

Plasma generation and processing of interstellar carbonaceous dust analogs

Interstellar (IS) dust analogs, based on amorphous hydrogenated carbon (a-C:H) were generated by plasma deposition in RF discharges of CH4 + He mixtures. The a-C:H samples were characterized by means of secondary electron microscopy (SEM), infrared (IR) spectroscopy and UV-visible reflectivity. DFT calculations of structure and IR spectra were also carried out. From the experimental data, atomic compositions were estimated. Both IR and reflectivity measurements led to similar high proportions (≈ 50%) of H atoms, but there was a significant discrepancy in the sp2/sp3 hybridization ratios of C atoms (sp2/sp3 = 1.5 from IR and 0.25 from reflectivity). Energetic processing of the samples with 5 keV electrons led to a decay of IR aliphatic bands and to a growth of aromatic bands, which is consistent with a dehydrogenation and graphitization of the samples. The decay of the CH aliphatic stretching band at 3.4 µm upon electron irradiation is relatively slow. Estimates based on the absorbed energy and on models of cosmic ray (CR) flux indicate that CR bombardment is not enough to justify the observed disappearance of this band in dense IS clouds.

Reaction of H + HONO in solid para-hydrogen: infrared spectrum of ˙ONH(OH)

Hydrogenation reactions in the N/O chemical network are important for an understanding of the mechanism of formation of organic molecules in dark interstellar clouds, but many reactions remain unknown.

Imaging the dynamics of ion–molecule reactions

A range of ion–molecule reactions have been studied in the last years using the crossed-beam ion imaging technique, from charge transfer and proton transfer to nucleophilic substitution and elimination.

Preferential Isomer Formation Observed in H3+ + CO by Crossed Beam Imaging

The proton transfer reaction H3(+) + CO is one of the cornerstone chemical processes in the interstellar medium. Here, the dynamics of this reaction have been investigated using crossed beam velocity map imaging. Formyl product cations are found to be predominantly scattered into the forward direction irrespective of the collision energy. In this process, a high amount of energy is transferred to internal product excitation. By fitting a sum of two distribution functions to the measured internal energy distributions, the product isomer ratio is extracted. A small HOC(+) fraction is obtained at a collision energy of 1.8 eV, characterized by an upper limit of 24% with a confidence level of 84%. At lower collision energies, the data indicate purely HCO(+) formation. Such low values are unexpected given the previously predicted efficient formation of both HCO(+) and HOC(+) isomers for thermal conditions. This is discussed in light of the direct reaction dynamics that are observed.

Relevance and Significance of Extraterrestrial Abiological Hydrocarbon Chemistry

Astrophysical observations show similarity of observed abiological "organics"-i.e., hydrocarbons, their derivatives, and ions (carbocations and carbanions)-with studied terrestrial chemistry. Their formation pathways, their related extraterrestrial hydrocarbon chemistry originating from carbon and other elements after the Big Bang, their parent hydrocarbon and derivative (methane and methanol, respectively), and transportation of derived building blocks of life by meteorites or comets to planet Earth are discussed in this Perspective. Their subsequent evolution on Earth under favorable "Goldilocks" conditions led to more complex molecules and biological systems, and eventually to humans. The relevance and significance of extraterrestrial hydrocarbon chemistry to the limits of science in relation to the physical aspects of evolution on our planet Earth are also discussed.

Methane ice photochemistry and kinetic study using laser desorption time-of-flight mass spectrometry at 20 K

Laser Desorption Post-Ionization Time-Of-Flight Mass Spectrometry is used to perform a systematic kinetic study on the pure methane photolysis in the condensed phase at 20 K and provides for the first time effective rate constants and branching ratios for primary processes leading to CH₃, CH₂, and CH radicals upon irradiation by VUV light in the 120–170 nm domain.