Search

This work introduces a cryovacuum apparatus used to investigate substances under near-space conditions. This device allows one to study the refractive index, infrared spectra, and density of substances that are condensed from the vapor phase onto a cooled substrate at temperatures ranging from 11 K to 300 K. Concurrently, the ultimate pressure of 0.1 nTorr can be obtained in the vacuum chamber. The introduced setup utilizes FTIR spectroscopy with a spectral measurement range of 400–7800 cm−1 and laser interference needed to determine the important physical and optical parameters. Several experiments allow us to stress that the data acquired using this apparatus are quite similar to those obtained by other researchers. Because of the non-directional deposition of substances from the vapor phase, the ice formed closely resembles the ice formed in space. This makes the introduced setup particularly useful. It is possible to use the presented cryovacuum apparatus to interpret data acquired in the course of astrophysical observations, allowing a researcher to determine the properties of space objects. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

Model calculations are performed to investigate the kinetic isotope effect of hydrogen and deuterium atom diffusion on hexagonal ice and amorphous solid water. Comparisons with experimental results by Kuwahata et al. (Phys. Rev. Lett., Sep. 2015, 115 (13), 133201) at 10 K are made. The experimentally derived kinetic isotope effect on amorphous solid water is reproduced by transition state theory. The experimentally found kinetic isotope effect on hexagonal ice is much larger than on amorphous solid water and is not reproduced by transition state theory. Additional calculations using model potentials are made for the hexagonal ice, but the experimental kinetic isotope effect is not fully reproduced. A strong influence of temperature is observed in the calculations. The influence of tunnelling is discussed in detail and related to the experiments. The calculations fully support the claims by the Kuwahata et al. (Phys. Rev. Lett., Sep. 2015, 115 (13), 133201) that on amorphous solid water the diffusion is predominantly by thermal hopping while on the polycrystalline ice tunnelling diffusion contributes significantly.

The degree of porosity in interstellar dust-grain material is poorly defined, although recent work has suggested that the grains could be highly porous. Aside from influencing the optical properties of the dust, porosity has the potential to affect the chemistry occurring on dust-grain surfaces, via increased surface area, enhanced local binding energies, and the possibility of trapping of molecules within the pores as ice mantles build up on the grains. Through computational kinetics simulations, we investigate how interstellar grain-surface chemistry and ice composition are affected by the porosity of the underlying dust-grain material. Using a simple routine, idealized three-dimensional dust-grains are constructed, atom by atom, with varying degrees of porosity. Diffusive chemistry is then simulated on these surfaces using the off-lattice microscopic Monte Carlo chemical kinetics model, MIMICK, assuming physical conditions appropriate to dark interstellar clouds. On the porous grain surface, the build-up of ice mantles, mostly composed of water, leads to the covering over of the pores, leaving empty pockets. Once the pores are completely covered, the chemical and structural behavior is similar to non-porous grains of the same size. The most prominent chemical effect of the presence of grain porosity is the trapping of molecular hydrogen, formed on the grain surfaces, within the ices and voids inside the grain pores. Trapping of H2 in this way may indicate that other volatiles, such as inert gases not included in these models, could be trapped within dust-grain porous structures when ices begin to form.

It was in ‘The Magellanic Cloud’ (1955) – a science fiction novel by Stanislaw Lem – that engineers travelling to another star noticed that their spacecraft for unknown reasons overheated. The cause had to be outside the spaceship, but obviously there was only emptiness, at least compared to terrestrial conditions. The space between the stars, the interstellar medium (ISM), however, is not completely empty and at the high speed of the spacecraft the cross-section with impacting particles, even from such a dilute environment, was found to be sufficient to cause an overheating. Today, 60 years later, the ISM has been studied in detail by astronomical observations, reproduced in dedicated laboratory experiments and simulated by complex astrochemical models. The space between the stars is, indeed, far from empty; it comprises gas, dust and ice and the molecules detected so far are both small (diatomics) and large (long carbon chains, PAHs and fullerenes), stable and reactive (radicals, ions, and excited molecules) evidencing an exotic and fascinating chemistry, taking place at low densities, low temperatures and experiencing intense radiation fields. Astrochemists explain the observed chemical complexity in space – so far 185 different molecules (not including isotopologues) have been identified – as the cumulative outcome of reactions in the gas phase and on icy dust grains. Gas phase models explain the observed abundances of a substantial part of the observed species, but fail to explain the number densities for stable molecules, as simple as water, methanol or acetonitrile – one of the most promising precursor species for the simplest amino acid glycine – as well as larger compounds such as glycolaldehyde, dimethylether and ethylene glycol. Evidence has been found that these and other complex species, including organic ones, form on icy dust grains that act as catalytic sites for molecule formation. It is here where particles ‘accrete, meet, and greet’ (i.e. freeze out, diffuse and react) upon energetic and non-energetic processing, such as irradiation by vacuum UV light, interaction with impacting particles (atoms, electrons and cosmic rays) or heating. This review paper summarises the state-of-the-art in laboratory based interstellar ice chemistry. The focus is on atom addition reactions, illustrating how water, carbon dioxide and methanol can form in the solid state at astronomically relevant temperatures, and also the formation of more complex species such as hydroxylamine, an important prebiotic molecule, and glycolaldehyde, the smallest sugar, is discussed. These reactions are particularly relevant during the ‘dark’ ages of star and planet formation, i.e. when the role of UV light is restricted. A quantitative characterization of such processes is only possible through dedicated laboratory studies, i.e. under full control of a large set of parameters such as temperature, atom-flux, and ice morphology. The resulting numbers, physical and chemical constants, e.g. barrier heights, reaction rates and branching ratios, provide information on the molecular processes at work and are needed as input for astrochemical models, in order to bridge the timescales typical for a laboratory setting to those needed to understand the evolutionary stages of the ISM. Details of the experiments as well as the astrochemical impact of the results are discussed. [ABSTRACT FROM PUBLISHER]

Abstract: We discuss the crystallinity and the temperature of water ice grains in the coma of comet C/2002 T7 (LINEAR) at 3.5AU from the Sun. The observed relative reflectance spectrum in J and H bands can be reproduced by using the Hapke’s model. Due to limited S/N ratios of the observed spectrum, however, we can not identify the phase (crystalline or amorphous states) of water ice. Both crystalline and amorphous water ices can explain the observed spectrum within the errors. If the water ice was in amorphous state, the cometary ices formed and/or condensed in the molecular cloud or in the solar nebula (at further than 25AU from the Sun). In contrast, if the cometary water ice was in crystalline state, the temperature of the icy grains in the coma could be estimated to be about 140–170K, which is consistent with the temperature of sublimating dirty water ice grains at 3.5AU. [Copyright &y& Elsevier]

The presence of H 2 O within differentiated terrestrial bodies in the inner Solar System is well established; however, the source(s) of this H 2 O and the time of its arrival to the inner Solar System is an area of active study. At present, the prevailing model for the origin of inner Solar System H 2 O calls upon carbonaceous chondrites as the source. This is largely based on reported observations that H- and N-isotopic compositions of differentiated planetary bodies are largely the same and within a range of values that overlaps with carbonaceous chondrites as opposed to comets or the Sun. In this contribution, we evaluate the efficacy of this model and other models for the origin of inner Solar System H 2 O by considering geochronological constraints on early Solar System history, constraints on primary building blocks of differentiated bodies based on nucleosynthetic isotope anomalies, and constraints from dynamical models of planet formation. In addition to H- and N-isotopic data, these constraints indicate that an interstellar source of H 2 O was present in the inner Solar System within the first 4 Ma of CAI formation. Furthermore, the most H 2 O-rich carbonaceous chondrites are unlikely to be the source of H 2 O for the earliest-formed differentiated bodies based on their minimally overlapping primary accretion windows and the separation of their respective isotopic reservoirs by Jupiter in the timespan of about 1–4 Ma after CAI formation. The presence of deuterium-rich, non-nebular H 2 O sources in the inner Solar System prior to the formation of carbonaceous chondrites or comets implies early contributions of interstellar ices to both the inner and outer Solar System portions of the protoplanetary disk. Evidence for this interstellar ice component in the inner Solar System may be preserved in LL chondrites and in the mantle of Mars. In contrast to the earlier-formed bodies within the inner Solar System, Earth's protracted accretion window may have facilitated incorporation of H 2 O in its interior from both the inner and outer Solar System, helping the Earth to become a habitable planet. • Interstellar ices were added to the inner and outer Solar System within 4 Ma of CAI. • LL chondrites and the martian interior record interstellar H-isotopic components. • Carbonaceous chondrites may not have supplied H 2 O to the angrite parent body or 4 Vesta. • Earth's protracted primary accretion window may have facilitated its habitability. [ABSTRACT FROM AUTHOR]