Solid-phase chemistry driven by energetic processing

Molecules in the solid phase have been detected in the line of sight of quiescent molecular clouds and star forming regions as icy mantles on dust grains. Although about 10 molecular species have been firmly identified in icy grain mantles, it is believed that many, also complex, species are present in the solid phase which are not detected due to the detection limits of infrared spectroscopy. It is generally accepted that some of the observed species (such as CO) freeze out from the gas phase while others (such as water and methanol) are formed on grains after surface reactions. Other species (such as CO2 and OCS), are not expected to freeze out in significant amount from the gas phase and grain surface models do not account for their observed abundance. It has been suggested that these molecules, along with other more complex species, are formed after energetic processing (i.e. cosmic ion and UV irradiation) of icy grain mantles. All these species are released to the gas-phase after desorption of icy mantles. Here we will present some recent laboratory experiments which show the formation of (complex) molecular species after energetic processing of simple ices. Icy targets have been processed by ion bombardment and UV photolysis both in separate experiments and recently, for the first time, simultaneously. When C-rich species are present in the initial ice, an organic refractory material is also formed

Hydrogen Isotopic Substitution Studies of the 2165 Wavenumber (4.62 Micron) "XCN" Feature Produced by Ion Bombardment

The interstellar 4.62 μm absorption band, commonly seen toward embedded protostellar objects, has not yet been unambiguously identified; here we report new results which further elucidate the components of the band carrier, which is often referred to in the literature as the "XCN" band due to previous implications of carbon and nitrogen. If the atmosphere of the early Earth was not overly reducing, as some studies indicate, production of prebiotic molecules containing the cyanogen bond would have been difficult. In that case, CN-bearing molecules, necessary for the origin of life, may have come primarily from extraterrestrial sources, and the interstellar medium may be an important source of those molecules. Laboratory studies show that energetic processing of ice mixtures containing H, C, N, and O atoms readily reproduce a band similar in peak position and profile to that seen in the interstellar spectra. Earlier isotopic labeling experiments clearly identified carbon, nitrogen, and oxygen as active participants of the XCN species. In this paper, results of ion bombardment of CH3OH : N2 and CD3OD : N2 ices are presented. A shift in band position resulting from deuterium substitution demonstrates that hydrogen is also a component of the carrier in the laboratory-produced 4.62 μm band. Irradiation of ices through ion bombardment allows the testing of mixtures which include N2, a possible source of the available nitrogen in dense cloud ices that cannot be probed through UV photolysis experiments

A new study of an old sink of sulfur in hot molecular cores: the sulfur residue

Sulfur appears to be depleted by an order of magnitude or more from its elemental abundance in star-forming regions. In the last few years, numerous observations and experiments have been performed in order to to understand the reasons behind this depletion without providing a satisfactory explanation of the sulfur chemistry towards high-mass star-forming cores. Several sulfur-bearing molecules have been observed in these regions, and yet none are abundant enough to make up the gas-phase deficit. Where, then, does this hidden sulfur reside? This paper represents a step forward in our understanding of the interactions among the various S-bearing species. We have incorporated recent experimental and theoretical data into a chemical model of a hot molecular core in order to see whether they give any indication of the identity of the sulfur sink in these dense regions. Despite our model producing reasonable agreement with both solid-phase and gas-phase abundances of many sulfur-bearing species, we find that the sulfur residue detected in recent experiments takes up only ~6 per cent of the available sulfur in our simulations, rather than dominating the sulfur budget.Comment: 13 pages, 6 colourful figures, accepted by MNRA

Integrated Near-Infrared Band Strengths of Solid CH4 and Its Mixtures with N2

We studied icy CH4 and its mixtures with N2 (temperature 16-40 K), using near-IR transmittance spectroscopy (1.0-3.6 μm), and monitoring the film growth using interference patterns of two lasers. We measured peak position, full width at half-maximum, and strengths of the methane bands, and density and real refractive index of the icy films. Results confirm and extend but also partially contradict previous studies on similar mixtures. Experimental data can be applied to interpret observations of solar system (trans-Neptunian objects) and interstellar ices, where methane and nitrogen are believed to be present. We predict the optical depths of two methane NIR bands in the line of sight of some dense molecular clouds

Synthesis of CO and CO2 Molecules by UV Irradiation of Water Ice-covered Hydrogenated Carbon Grains

We present the results of UV irradiation with Lyα photons of carbon grains with a water ice cap at 11 K. Formation of CO and CO2 molecules takes place during irradiation. An estimation of the formation cross section of these molecules by Lyα photons has been obtained from the intensity increase of their infrared stretching bands as a function of the photon fluence. The fraction of carbon in the grains converted to CO and CO2 by UV photons is 0.06 and 0.05, respectively. The spectral profile of the CO stretching feature and that of the CO2 bending mode indicate a polar environment for these molecules. On the basis of the present laboratory results and those obtained in previous work on ion irradiation of similar samples, it has been possible to estimate the contribution of polar CO and CO2 produced on carbon grains by energetic processing to the observed column densities of these molecules for dense clouds whose visual extinction is known. A significant amount of polar CO and CO2 is produced through the mechanism we have studied. Furthermore, we have found that the laboratory profile of the bending band of CO2 produced on carbon grains is compatible with that observed toward the field star Elias 16

Ion Implantation and Chemical Cycles in the Icy Galilean Satellites

An essential requisite for the appearance and permanence of life on Earth is the onset of a continuous “cycling” of some key atoms and molecules. Cycling of elements probably also occurs on other objects and is driven by biological or a-biological processing. Here we investigate the cycling of some species in the icy Galilean satellites that are exposed to the intense fluxes of energetic particles coming from the Jupiter magnetosphere. Among the most studied effects of particle bombardment, there is the production of molecules not originally present in the sample. These newly synthesized species are irradiated as well and in some circumstances can re-form the original species, giving rise to a “cycle”. Here we discuss the cycling of some atoms (C, N, O, S) incorporated in molecules observed on the surface of the icy Galilean satellites. The results indicate that cycling of carbon atoms starts with solid elemental carbon. Irradiated in the presence of water ice, carbon dioxide is produced and forms carbonic acid and other organics whose irradiation re-produces carbon dioxide and solid carbon. The effect on nitrogen atoms is limited to a continuous cycle among nitrogen oxides (e.g. NO2 produces NO, and N2O). Oxygen is mostly incorporated in water ice. When irradiated, the large majority of the water molecular fragments recombine to re-form water molecules. The sulfur cycle occurs among SO2 (that cannot be produced by ion irradiation only), sulfuric acid and elemental sulfur. The results are discussed in view of their relevance to the expected space observations of the JWST telescope (NASA, ESA, CSA) and the JUICE (ESA) spacecraft

Natural thermal plasters for fibre-composite matrices. Structural-energy-environmental analysis

The article presents the first results of MIRACLE research, aimed at designing, testing, and implementing innovative reinforcement systems with bio-composite matrix, with additives containing natural thermal-plasters, usable in the restoration of residential buildings created before 1945. Starting from a brief description of the properties of fibre-reinforced cement organic matrices, supported by a survey of international research aimed at developing innovative methodologies, systems, and components used to improve the energy and mechanical performances of listed historic buildings, the most suitable thermal-plasters will be analysed (among those existing on the Italian market), identifying the performance characteristics both in terms of mechanic and thermal and environmental sustainability

Cosmic ray processing of N2-containing interstellar ice analogues at dark cloud conditions

N2 is believed to lock considerable part of nitrogen elemental budget and, therefore, to be one of the most abundant ice constituent in cold dark clouds. This laboratory-based research utilizes high energetic processing of N2 containing interstellar ice analogues using 200 keV H+ and He+ ions that mimics cosmic ray processing of the interstellar icy grains. It aims to investigate the formation of (iso)cyanates and cyanides in the ice mantles at the conditions typical for cold dark clouds and prestellar cores. Investigation of cosmic ray processing as a chemical trigger mechanism is explained by the high stability of N2 molecules that are chemically inert in most of the atom- and radical-addition reactions and cannot be efficiently dissociated by cosmic ray induced UV-field. Two sets of experiments are performed to closer address solid-state chemistry occurring in two distinct layers of the ice formed at different stages of dark cloud evolution, i.e. `H2O-rich' and `CO-rich' ice layers. Formation of HNCO and OCN- is discussed in all of the performed experiments. Corresponding kinetic curves for HNCO and OCN- are obtained. Furthermore, a feature around 2092 cm-1 assigned to the contributions of 13CO, CN-, and HCN is analysed. The kinetic curves for the combined HCN/CN- abundance are derived. In turn, normalized formation yields are evaluated by interpolation of the obtained results to the low irradiation doses relevant to dark cloud stage. The obtained values can be used to interpret future observations towards cold dark clouds using James Webb Space Telescope

Exploring Refractory Organics in Extraterrestrial Particles

The origin of organic compounds detected in meteorites and comets, some of which could have served as precursors of life on Earth, remains an open question. The aim of the present study is to make one more step in revealing the nature and composition of organic materials of extraterrestrial particles by comparing infrared spectra of laboratory-made refractory organic residues to spectra of cometary particles returned by the Stardust mission, interplanetary dust particles, and meteorites. Our results reinforce the idea of a pathway for the formation of refractory organics through energetic and thermal processing of molecular ices in the solar nebula. There is also the possibility that some of the organic material had formed already in the parental molecular cloud before it entered the solar nebula. The majority of the IR “organic” bands of the studied extraterrestrial particles can be reproduced in the spectra of the laboratory organic residues. We confirm the detection of water, nitriles, hydrocarbons, and carbonates in extraterrestrial particles and link it to the formation location of the particles in the outer regions of the solar nebula. To clarify the genesis of the species, high-sensitivity observations in combination with laboratory measurements like those presented in this paper are needed. Thus, this study presents one more piece of the puzzle of the origin of water and organic compounds on Earth and motivation for future collaborative laboratory and observational projects

Astrobiology studies and extraterrestrial sample analysis at the Laboratory for Experimental Astrophysics - Catania

Energetic ions (galactic cosmic rays, solar wind, energetic solar ions) and UV photons are believed to significantly contribute to the evolution of solid matter in astrophysical environments. At the Laboratory for Experimental Astrophysics at INAF-Osservatorio Astrofisico di Catania samples are exposed to space conditions such as high vacuum, low temperature (15-300 K), UV irradiation (266 nm and Lyman-alpha at 121.6 nm) and fast ion bombardment (60-400 keV) and are analyzed in situ by Infrared and Raman spectroscopy. Ices, carbons and silicates have been processed and analyzed. In addition, extraterrestrial dust particles (e.g. IDPs, cometary dust particles, and meteorites) have been characterized by non destructive techniques such as micro-Raman and UV-Vis-IR spectroscopy. Furthermore, spectra of extraterrestrial samples have been compared to spectra of laboratory analogues. Here we present some of the most recent results relevant to Astrobiology and the ongoing upgrade of the experimental set-up