Showing papers by "Maria Elisabetta Palumbo published in 2017"

Thermal and energetic processing of astrophysical ice analogues rich in SO2

Abstract: Context. Sulfur is an abundant element in the cosmos and it is thus an important contributor to astrochemistry in the interstellar medium and in the solar system. Astronomical observations of the gas and of the solid phases in the dense interstellar/circumstellar regions have evidenced that sulfur is underabundant. The hypothesis to explain such a circumstance is that it is incorporated in some species in the solid phase (i.e. as frozen gases and/or refractory solids) and/or in the gas phase, which for different reasons have not been observed so far. Aims. Here we wish to give a contribution to the field by studying the chemistry induced by thermal and energetic processing of frozen mixtures of sulfur dioxide (one of the most abundant sulfur-bearing molecules observed so far) and water. Methods. We present the results of a series of laboratory experiments concerning thermal processing of different H 2 O:SO 2 mixtures and ion bombardment (30 keV He + ) of the same mixtures. We used in situ Fourier transform infrared (FTIR) spectroscopy to investigate the induced effects. Results. The results indicate that ionic species such as HSO 3 − , HSO 4 − , and S 2 O 5 2− are easily produced. Energetic processing also produces SO 3 polymers and a sulfurous refractory residue. Conclusions. The produced ionic species exhibit spectral features in a region that, in astronomical spectra of dense molecular clouds, is dominated by strong silicate absorption. However, such a dominant feature is associated with some spectral features, some of which have not yet been identified. We suggest adding the sulfur-bearing ionic species to the list of candidates to help explain some of those features. In addition, we suggest that once expelled in the gas phase by sublimation, due to the temperature increase, and/or by non-thermal erosion those species would constitute a class of molecular ions not detected so far. We also suggest that molecular sulfur-bearing ions could be present on the surfaces and/or in the atmospheres of several objects in the solar system, for example icy satellites of the giant planets and comets.

Infrared study on the thermal evolution of solid state formamide

Abstract: Laboratory experiments have shown that the energetic processing, i.e. ion bombardment and UV photolysis, of interstellar grain mantles and cometary surfaces is efficient in the production of formamide. To explain its presence in the gas-phase in these astrophysical environments, a desorption mechanism has to be taken into account. In this work we show experimental results on the thermal evolution of formamide when deposited at 17 K as pure and in mixture with water or carbon monoxide. In these samples, we observed formamide desorption at 220 K. Moreover, we discuss its synthesis in a mixture containing molecular nitrogen, methane and water (N2:CH4:H2O) deposited at 17 K and bombarded with 200 keV H+. Heating the sample, we observed that the newly formed formamide remains trapped in the refractory residue produced after the ion bombardment up to 296 K. To analyse the samples we used Fourier transform-infrared spectroscopy (FT-IR) that allowed us to study the infrared spectra between the deposition and the complete desorption of formamide. Here we discuss the experimental results in view of their astrophysical relevance.

Thermal and energetic processing of astrophysical ice analogues rich in SO$_2$

Abstract: Sulfur is an abundant element in the cosmos and it is thus an important contributor to astrochemistry in the interstellar medium and in the Solar System. Astronomical observations of the gas and of the solid phases in the dense interstellar/circumstellar regions have evidenced that sulfur is underabundant. The hypothesis to explain such a circumstance is that it is incorporated in some species in the solid phase (i.e. as frozen gases and/or refractory solids) and/or in the gas phase, which for different reasons have not been observed so far. Here we wish to give a contribution to the field by studying the chemistry induced by thermal and energetic processing of frozen mixtures of sulfur dioxide (one of the most abundant sulfur-bearing molecules observed so far) and water. We present the results of a series of laboratory experiments concerning thermal processing of different H2O:SO2 mixtures and ion bombardment 30 keV He$^+$ of the same mixtures. We used in situ FTIR spectroscopy to investigate the induced effects. The results indicate that ionic species such as HSO$_{3}^{-}$, HSO$_{4}^{-}$, and S$_2$O$_{5}^{2-}$ are easily produced. Energetic processing also produces SO$_3$ polymers and a sulfurous refractory residue. The produced ionic species exhibit spectral features in a region that, in astronomical spectra of dense molecular clouds, is dominated by strong silicate absorption. However, such a dominant feature is associated with some spectral features, some of which have not yet been identified. We suggest adding the sulfur-bearing ionic species to the list of candidates to help explain some of those features.

The profile of the bending mode band in solid CO2

Abstract: Context. Solid carbon dioxide (CO2 ) is one of the most abundant species detected in icy grain mantles in dense molecular clouds. Its identification is based on the comparison between astronomical and laboratory spectra. In the past 30 yr the profile of solid CO2 infrared absorption bands has been extensively studied experimentally, however, the debate on the structure (amorphous versus crystalline) of CO2 samples obtained in laboratory by the thin-film technique is still open.Aims. The aim of this work is to investigate if the presence of the double peak feature in the profile of the CO2 bending mode band is related to the crystalline or amorphous structure of the sample.Methods. We performed new laboratory experiments depositing CO2 under ultra high vacuum (UHV) conditions at 17 K. We investigated, using infrared transmission spectroscopy, the influence of various experimental parameters on the profile of the CO2 bands, namely deposition rate, sample thickness, annealing, and presence of H2 O, CH3 OH or CO co-deposited with CO2 . Results. We found that, within experimental uncertainties, under UHV conditions the profile of the CO2 bands in pure solid samples does not depend on the deposition rate or the sample thickness in the ranges investigated. In all cases the bending mode band profile shows a double peak (at 660 and 655 cm-1 ). The spectra also show the Fermi resonance features that cannot be active in crystalline samples. On the other hand, when a small fraction of H2 O or CH3 OH is co-deposited with CO2 the double peak is not observed while it is observed when a CO2 :CO mixture is considered. Furthermore, we measured the density of solid CO2 and the refractive index (at 543.5 nm) at 17 K and at 70 K: ρ (17 K)= 1.17 g cm-3 , ρ (70K)= 1.49 g cm-3 , n (17K)= 1.285, and n (70K)= 1.372. Conclusions. Our experimental results indicate that the presence of the double peak in the profile of the bending mode band is not an indication of a crystalline structure of the sample and they do not exclude the presence of amorphous solid CO2 in space.

Laboratory Studies of Methane and Its Relationship to Prebiotic Chemistry

Abstract: To examine how prebiotic chemical evolution took place on Earth prior to the emergence of life, laboratory experiments have been conducted since the 1950s. Methane has been one of the key molecules in these investigations. In earlier studies, strongly reducing gas mixtures containing methane and ammonia were used to simulate possible reactions in the primitive atmosphere of Earth, producing amino acids and other organic compounds. Since Earth's early atmosphere is now considered to be less reducing, the contribution of extraterrestrial organics to chemical evolution has taken on an important role. Such organic molecules may have come from molecular clouds and regions of star formation that created protoplanetary disks, planets, asteroids, and comets. The interstellar origin of organics has been examined both experimentally and theoretically, including laboratory investigations that simulate interstellar molecular reactions. Endogenous and exogenous organics could also have been supplied to the primitive ocean, making submarine hydrothermal systems plausible sites of the generation of life. Experiments that simulate such hydrothermal systems where methane played an important role have consequently been conducted. Processes that occur in other Solar System bodies offer clues to the prebiotic chemistry of Earth. Titan and other icy bodies, where methane plays significant roles, are especially good targets. In the case of Titan, methane is both in the atmosphere and in liquidospheres that are composed of methane and other hydrocarbons, and these have been studied in simulation experiments. Here, we review the wide range of experimental work in which these various terrestrial and extraterrestrial environments have been modeled, and we examine the possible role of methane in chemical evolution

SERPING1 mRNA overexpression in monocytes from HIV+ patients.

Abstract: The HIV-1 virus activates the complement system, an essential element of the immune system. SERPING1 is a protease inhibitor that disables C1r/C1s in the C1 complex of the classical complement pathway. In this paper, we performed an analysis of several microarrays deposited in GEO dataset to demonstrate that SERPING1 mRNA is modulated in CD14+ monocytes from HIV-1-infected individuals. In addition, data were validated on monocytes isolated from seronegative healthy volunteers, treated with IFNs. Our analysis shows that SERPING1 mRNA is overexpressed in monocytes from HIV-1+ patients and the expression levels correlate positively with viral load and negatively with the CD4+ T-cell count. Of note, anti-retroviral therapy is able to reduce the levels of SERPING1 mRNA, ex vivo. In addition, we found that 30% of the SERPING1 genes network is upregulated in monocytes from HIV-1+ patients. Noteworthy, the expression levels of IFITM1—an antiviral molecule belonging to the genes network—correlate positively with SERPING1 expression. Interestingly, the monocytes treatment with IFN-gamma, IFN-beta and IFN-alpha significantly upregulates the SERPING1 mRNA expression levels. From the outcome of our investigation, it is possible to conclude that SERPING1 and its network serve as important components of the innate immune system to restrict HIV-1 infection.

Solid CO2 in quiescent dense molecular clouds - Comparison between Spitzer and laboratory spectra

Abstract: Context. Carbon dioxide (CO2 ) is one of the most abundant species detected in icy grain mantles in star forming regions. Laboratory experiments have shown that CO2 molecules are efficiently formed in the solid state under interstellar conditions. Specifically, solid CO2 can be formed through energetic (e.g. UV photolysis, electron and ion bombardment) and non-energetic mechanisms (atom-addition reactions).Aims. Here we investigate the role of low-energy cosmic-ray bombardment in the formation of solid CO2 in quiescent dense molecular clouds.Methods. We performed laboratory experiments to study the formation of CO2 after ion irradiation with 200 keV H+ of astrophysical relevant ice mixtures. Laboratory spectra are used to fit the profile of the CO2 bending mode band observed at about 15.2 μ m (660 cm-1 ) by the Spitzer Space Telescope in the line of sight to background sources.Results. From a qualitative point of view, good fits to observations are obtained by considering either three or four laboratory components. From a quantitative point of view, a better result is obtained with four components, i.e. when a spectrum of CO2 formed after ion irradiation of CH3 OH ice is added to the fitting procedure.Conclusions. Our results support the hypothesis that energetic processing of icy grain mantles is an efficient formation mechanism of CO2 ice also in quiescent dark cloud regions, and indirectly suggest the presence of CH3 OH in icy grain mantles in interstellar cold regions.

Sputtering of sodium and potassium from nepheline: Secondary ion yields and velocity spectra

Abstract: Silicates are the dominant surface material of many Solar System objects, which are exposed to ion bombardment by solar wind ions and cosmic rays. Induced physico-chemical processes include sputtering which can contribute to the formation of an exosphere. We have measured sputtering yields and velocity spectra of secondary ions ejected from nepheline, an aluminosilicate thought to be a good analogue for Mercury's surface, as a laboratory approach to understand the evolution of silicate surfaces and the presence of Na and K vapor in the exosphere. Experiments were performed with highly charged ion beams (keV/u–MeV/u) delivered by GANIL using an imaging XY-TOF-SIMS device under UHV conditions. The fluence dependence of sputtering yields gives information about the evolution of surface stoichiometry during irradiation. From the energy distributions N(E) of sputtered particles, the fraction of particles which could escape from the gravitational field of Mercury, and of those falling back and possibly contributing to populate the exosphere can be roughly estimated.