Residue from vacuum ultraviolet irradiation of benzene ices: Insights into the physical structure of astrophysical dust

We have irradiated benzene ices deposited at 4 K on a cold, interstellar dust analog with vacuum ultraviolet (9 eV) irradiation for periods lasting from several hours to nearly a day, after which the irradiated ice was warmed to room temperature. Vacuum ultraviolet photoabsorption spectra of the aromatic residue left at room temperature were recorded and showed the synthesis of benzene derivatives. The residue was also imaged using an electron microscope and revealed crystals of various sizes and shapes. The result of our experiments suggests such geometrically shaped dust particles may be a key component of interstellar dust

VUV Photoabsorption of Thermally Processed Carbon Disulfide and Ammonia Ice Mixtures - Implications for Icy Objects in the Solar System

Many icy bodies in the solar system have been found to contain a rich mixture of simple molecules on their surfaces. Similarly, comets are now known to be a reservoir of molecules ranging from water to amides. The processing of planetary/cometary ices leads to the synthesis of more complex molecules some of which may be the harbingers of life. Carbon disulphide (CS2) and ammonia (NH3) are known to be present on many icy satellites and comets. Reactions involving CS2 and NH3 may lead to the formation of larger molecules that are stable under space conditions. In this paper we present temperature dependent VUV spectra of pure CS2 in the ice phase, and of CS2 and NH3 ices deposited as (i) layered, and (ii) mixed ices at 10 K and warmed to higher temperatures until their sublimation. Pure CS2 ice is found to have a broad absorption in the VUV region, which is unique for a small molecule in the ice phase. In layered and mixed ices, the molecules tend to affect the phase change and sublimation temperature of each other and also leave behind a form of CS2−NH3 complex after thermal annealing. This study of CS2-NH3 ice systems in layered and mixed configurations would support the detection of these species/complexes in mixed molecular ices analogous to that on planetary and cometary surfaces

Mid-IR and VUV spectroscopic characterisation of thermally processed and electron irradiated CO2 astrophysical ice analogues

The astrochemistry of CO2 ice analogues has been a topic of intensive investigation due to the prevalence of CO2 throughout the interstellar medium and the Solar System, as well as the possibility of it acting as a carbon feedstock for the synthesis of larger, more complex organic molecules. In order to accurately discern the physico-chemical processes in which CO2 plays a role, it is necessary to have laboratory-generated spectra to compare against observational data acquired by ground- and space-based telescopes. A key factor which is known to influence the appearance of such spectra is temperature, especially when the spectra are acquired in the infrared and ultraviolet. In this present study, we describe the results of a systematic investigation looking into: (i) the influence of thermal annealing on the mid-IR and VUV absorption spectra of pure, unirradiated CO2 astrophysical ice analogues prepared at various temperatures, and (ii) the influence of temperature on the chemical products of electron irradiation of similar ices. Our results indicate that both mid-IR and VUV spectra of pure CO2 ices are sensitive to the structural and chemical changes induced by thermal annealing. Furthermore, using mid-IR spectroscopy, we have successfully identified the production of radiolytic daughter molecules as a result of 1 keV electron irradiation and the influence of temperature over this chemistry. Such results are directly applicable to studies on the chemistry of interstellar ices, comets, and icy lunar objects and may also be useful as reference data for forthcoming observational missions

Large global variations in measured airborne metal concentrations driven by anthropogenic sources

10.1038/s41598-020-78789-yScientific Reports1012181