Interstellar Silicate Analogs for Grain-Surface Reaction Experiments: Gas-Phase Condensation and Characterization of the Silicate Dust Grains

Sabri, T.; Gavilan, Lisseth; Jäger, Cornelia; Lemaire, J. L.; Vidali, Gianfranco; Mutschke, H.; Henning, Thomas

doi:10.1088/0004-637x/780/2/180

Cited by 31 publications

(27 citation statements)

References 31 publications

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“…1. A more detailed description of the experimental procedure is given in Jäger et al (2008) and Sabri et al (2014). The final thickness of the deposits on either KBr or silicon substrates were in the range of around 120 nm controlled by a microbalance.…”

Section: Preparation Of Carbon Grain Samplesmentioning

confidence: 99%

A laboratory study of ion-induced erosion of ice-covered carbon grains

Sabri

Baratta

Jäger

et al. 2015

A&A

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Context. It has been confirmed that solid carbon dioxide (CO 2 ) is abundantly present along the line of sight to quiescent clouds and star-forming regions via space IR observations with ISO-SWS and Spitzer Space Telescope. Since CO 2 has low abundance in the gas-phase, the assumption is that it is synthesized on grains after energetic processing of icy mantles and surface reactions. Aims. The role of solid carbon is investigated as a reservoir for molecule formation and structural modifications of the material with and without an ice layer upon ion bombardment. Methods. A gas-phase condensation technique was used to prepare a layer of 13 C amorphous grains. These grains were covered with H 2 O and O 2 ice and finally bombarded with 200 keV protons. The formation of new molecular species was analyzed using IR spectroscopy. The formation cross sections of solid 13 CO and 13 CO 2 were determined from the increase in the column density as a function of the fluence. In addition, bare carbon grains were bombarded with a comparable fluence of protons to study the processing of the grains without ice layer. Imaging techniques such as transmission electron microscopy were used to monitor the changes in the structure. Results. CO and CO 2 were formed efficiently at the interface between ice and solid carbon grains at the expense of solid carbon, leading to strong grain erosion. Given the initial thickness of our C-samples (about 120 nm), this resulted in an erosion of about 50% after 200 keV proton bombardment with 6.76 × 10 16 ions/cm 2 . The column density of CO and CO 2 follows an exponential trend as a function of the irradiation fluence. The asymptotic values obtained when O 2 ice is deposited on top of the carbon grains are about one order of magnitude higher than the values obtained when H 2 O ice is deposited on the solid carbon layer. The carbon grains were strongly graphitized upon ion bombardment in a surface layer. Less graphitization accompanied by the formation of fullerene molecules and structures from cage fragments present in the original material were observed beneath the graphitic layer. Conclusions. The formation of CO and CO 2 at the expense of solid carbon strongly restricts the lifetime of the solid carbon material and may influence the formation of more complex molecules in astrophysical environments. Graphitization of carbonaceous grains upon ion bombardment affect the spectral properties of the carbon grains in particular in the far-IR range.

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Section: Preparation Of Carbon Grain Samplesmentioning

confidence: 99%

A laboratory study of ion-induced erosion of ice-covered carbon grains

Sabri

Baratta

Jäger

et al. 2015

A&A

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“…Highly advanced and often specifically dedicated laboratory techniques have been applied in many laboratories in order to produce interstellar dust analogs. For amorphous silicates, this includes, e.g., glass melting and quenching [21,14,58], the sol-gel process [10,23,64,9], amorphization by ion irradiation [12,24,4], and gas-phase condensation from vapors in oxidizing or inert atmospheres [11,57,19,31,53]. Gas-phase condensation is the primary technique for making carbonaceous dust analogs, with several methods to vaporize solid carbon thermally or by laser ablation [32,6,56,28]) or to introduce reactions in molecular precursors (e.g., by plasma pyrolysis [54] or laser-induced gas pyrolysis [55,35,25]).…”

Section: Laboratory Analogs Of Ism Dustmentioning

confidence: 99%

Optical Properties of Interstellar Dust from Cosmic Dust Analogs Studied in the Lab

Mutschke¹

2014

Proceedings of the Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013)

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In the past years, cosmic dust research has taken great advantage from the laboratory efforts to investigate the properties of analog materials such as amorphous magnesium/iron silicates and various forms of carbon. Optical properties are particularly important as they provide the link to observations and need to be incorporated into models in the form of dust opacities. Laboratory investigation of dust opacities has to cover a wide wavelength range from the UV to the millimeter wavelength range and to study the temperature dependence of the electromagnetic excitation processes governing the optical response. For understanding the underlying physics, a detailed knowledge of the microscopic structure is required, which in turn may allow predictions for dust in cosmic environments, being subject to continuous structural modifications. Given the complexity of amorphous structures, our understanding of the optical properties of interstellar dust is still incomplete. In particular, the opacity outside the strong fundamental excitations of the electron and phonon system are not yet very well constrained, but even some of the strong bands such as the π-π ⋆ transition band of carbonaceous dust and its relation to the interstellar 217.5 nm extinction feature still require closer investigation. In this respect, it is crucial to develop further the structural analysis of such amorphous structures, and to find the relation to optical properties. This review intends to summarize the current state of these efforts.

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“…Herbst et al (2005) reported theoretical studies of chemical reactions on interstellar grains and verified efficient formation of H2 from atomic hydrogen over a wide temperature range on inhomogeneous surfaces. The formation of molecular hydrogen specifically on silicates has been studied in detail with the rotational population distribution of H2 determined (Williams & Cecci-Pestellini 2016;Sabri et al 2014;Gavilan et al 2014). Reactions involving atoms other than hydrogen include work described by Anders et al (1973Anders et al ( , 1974 who reviewed the catalytic reactions of CO, H2 and NH3 on silicate and carbonate grain surfaces leading to the formation of small organic molecules as found in meteorites, the products including alcohols, aldehydes, ketones, ethers and esters.…”

Section: Introductionmentioning

confidence: 99%