EXPERIMENTAL STUDY OF CO
                    <sub>2</sub>
                    FORMATION BY SURFACE REACTIONS OF NON-ENERGETIC OH RADICALS WITH CO MOLECULES

Oba, Yasuhiro; Watanabe, Naoki; Kouchi, Akira; Hama, Tetsuya; Pirronello, V.

doi:10.1088/2041-8205/712/2/l174

Cited by 108 publications

(150 citation statements)

References 42 publications

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“…A similar conclusion is obtained by applying the same calculations to the fit of the CO 2 bending mode towards the field star Elias 16 shown by Mennella et al (2006). Although these are only two sources, this result to be confirmed along the line of sight to different quiescent clouds gives an indirect indication that CO 2 can also be formed in a early cloud stage through a different mechanism than for cosmic ray irradiation (e.g., surface reactions induced by non-energetic mechanisms; Oba et al 2010;Ioppolo et al 2011;Noble et al 2011). In a later stage, when ices are exposed to higher UV and cosmic ray doses, the total abundance of CO 2 is strongly affected by energetic formation mechanisms.…”

Section: Observational Constraintssupporting

confidence: 54%

“…This complex can directly dissociate, forming solid CO 2 and leaving an H atom, or can be stabilized by intramolecular energy transfer to the ice surface and eventually react with an incoming H atom in a barrierless manner to form CO 2 and H 2 or other products with a purely statistical branching ratio (Goumans et al 2008). Recently, several independent experimental studies have shown that reaction 3 is an efficient surface CO 2 formation channel without energetic input (i.e., Oba et al 2010;Ioppolo et al 2011;Noble et al 2011). Moreover, reaction 3 can explain the observed formation link between CO 2 and H 2 O ice under interstellar conditions, since OH radicals are involved in the reaction scheme, and water can be efficiently formed through reactions OH + H and OH + H 2 (e.g., Romanzin et al 2011;Oba et al 2012).…”

Section: Introductionmentioning

confidence: 99%

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Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

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Context. Solid interstellar CO 2 is an abundant component of ice dust mantles. Its ubiquity towards quiescent molecular clouds, as well as protostellar envelopes, has recently been confirmed by the IRS (InfraRed Spectrograph) aboard the Spitzer Space Telescope. Although it has been shown that CO 2 cannot be efficiently formed in the gas phase, the CO 2 surface formation pathway is still unclear. To date several CO 2 surface formation mechanisms induced by energetic (e.g., UV photolysis and cosmic ray irradiation) and nonenergetic (e.g., cold atom addition) input have been proposed. Aims. Our aim is to investigate the contribution of cosmic ray irradiation to the formation of CO 2 in different regions of the interstellar medium (ISM). To achieve this goal we compared quantitatively laboratory data with the CO 2 bending mode band profile observed towards several young stellar objects (YSOs) and a field star by the Spitzer Space Telescope. Methods. All the experiments presented here were performed at the Laboratory for Experimental Astrophysics in Catania (Italy). The interstellar relevant samples were all irradiated with fast ions (30−200 keV) and subsequently annealed in a stainless steel high vacuum chamber (P < 10 −7 mbar). Chemical and structural modifications of the ice samples were monitored by means of infrared spectroscopy. Laboratory spectra were then used to fit some thirty observational spectra.Results. A qualitative analysis shows that a good fit can be obtained with a minimum of two components. The choice of the laboratory components is based on the chemical-physical condition of each source. A quantitative analysis of the sources with known visual extinction (A V ) and methanol abundances highlights that the solid carbon dioxide can be efficiently and abundantly formed after ion irradiation of interstellar ices in all the selected YSOs in a time compatible with cloud lifetimes (3 × 10 7 years). Only in the case of field stars can the expected CO 2 column density formed upon energetic input not explain the observed abundances. This result, to be confirmed along the line of sight to different quiescent clouds, gives an indirect indication that CO 2 can also be formed in an early cloud stage through surface reactions induced by non-energetic mechanisms. In a later stage, when ices are exposed to higher UV and cosmic ray doses, the CO 2 total abundance is strongly affected by energetic formation mechanisms. Conclusions. Our results indicate that energetic processing of icy grain mantles significantly contribute to the formation of solid phase interstellar CO 2 .

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Section: Observational Constraintssupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

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“…A fast conversion of C into CO is also consistent with the CH 4 /H 2 O versus H 2 O anti-correlation toward lines of sight with low H 2 O column densities ( §3.7); it suggests that CH 4 forms more efficiently in the very beginning of H 2 O formation compared to when the bulk of H 2 O ice forms at slightly higher extinctions. The bulk of H 2 O formation is instead associated with continuous formation of CO 2 , probably from CO+OH (Oba et al 2010;Ioppolo et al 2011); the CO 2 :H 2 O abundance barely varies from source to source in the low-mass protostellar sample ( §3.3). H 2 O and CO 2 ice mapping confirms this scenario (Bergin et al 2005), as do the similar CO 2 abundances toward cloud cores and protostars ( §3.5).…”

Section: Ice Evolution: Early and Late Pre-stellar Ice Formationmentioning

confidence: 99%

THESPITZERICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS

Öberg

Boogert

Pontoppidan

et al. 2011

ApJ

481

338

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Ices regulate much of the chemistry during star formation and account for up to 80% of the available oxygen and carbon. In this paper, we use the Spitzer c2d ice survey, complimented with data sets on ices in cloud cores and high-mass protostars, to 1 Hubble Fellow 2 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands 3 Max Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstr.1, 85748 Garching, Germany -2 -determine standard ice abundances and to present a coherent picture of the evolution of ices during low-and high-mass star formation. The median ice composition H 2 O:CO:CO 2 :CH 3 OH:NH 3 :CH 4 :XCN is 100:29:29:3:5:5:0.3 and 100:13:13:4:5:2:0.6 toward low-and high-mass protostars, respectively, and 100:31:38:4:-:-:-in cloud cores. In the low-mass sample, the ice abundances with respect to H 2 O of CH 4 , NH 3 , and the component of CO 2 mixed with H 2 O typically vary by <25%, indicative of co-formation with H 2 O. In contrast, some CO and CO 2 ice components, XCN and CH 3 OH vary by factors 2-10 between the lower and upper quartile. The XCN band correlates with CO, consistent with its OCN − identification. The origin(s) of the different levels of ice abundance variations are constrained by comparing ice inventories toward different types of protostars and background stars, through ice mapping, analysis of cloud-to-cloud variations, and ice (anti-)correlations. Based on the analysis, the first ice formation phase is driven by hydrogenation of atoms, which results in a H 2 O-dominated ice. At later prestellar times, CO freezes out and variations in CO freeze-out levels and the subsequent CO-based chemistry can explain most of the observed ice abundance variations. The last important ice evolution stage is thermal and UV processing around protostars, resulting in CO desorption, ice segregation and formation of complex organic molecules. The distribution of cometary ice abundances are consistent with with the idea that most cometary ices have a protostellar origin.

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“…This approach makes it possible to derive fundamental and molecule specific parameters, like reaction rates and diffusion barriers, which can then be included in astrochemical models to simulate the ice evolution under much longer timescales (10 5 years) than accessible in the laboratory (\1 day). The work presented in the next section follows a bottom-up approach and summarizes a representative sample of relevant experiments (e.g., Watanabe and Kouchi 2002;Watanabe et al 2004Watanabe et al , 2006Fuchs et al 2009;Miyauchi et al 2008;Ioppolo et al 2008Ioppolo et al , 2010Ioppolo et al , 2011aMatar et al 2008;Oba et al 2009Oba et al , 2010Cuppen et al 2010;Mokrane et al 2009;Romanzin et al 2011;Ö berg et al 2009). These experiments prove that species like H 2 CO, CH 3 OH and H 2 O can be formed at low temperatures by simple hydrogenation (i.e., without the need for thermal, UV or cosmic ray processing) and provide the basic molecular data to simulate their formation on astronomical timescales (e.g., Cuppen et al 2009), even though the ice as a whole is not representative for a realistic astronomical ice.…”

Section: Bottom-up Versus Top-down Approachmentioning

confidence: 99%

Surface formation routes of interstellar molecules: hydrogenation reactions in simple ices

Ioppolo

Cuppen

Linnartz

2011

Rend. Fis. Acc. Lincei

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It has been a long standing problem in astrochemistry to explain how molecules can form in a highly dilute environment such as the interstellar medium. In recent years it has become clear that not only ion/radical-molecule gas-phase reactions, but also solid state reactions on icy dust grains play an important role in the formation of new species. In order to investigate the underlying processes, laboratory based experiments are needed to simulate surface reactions induced by photon (UV) processing or particle (atom, cosmic ray, electron) bombardment of interstellar ice analogs. Here, the latest research performed on SURFace REaction SImulation DEvice (SURFRESIDE), one of the ultra-high vacuum setups in the Sackler Laboratory for Astrophysics in Leiden is reviewed. The focus is on hydrogenation, i.e., H-atom addition reactions in interstellar ice analogs for astronomically relevant temperatures. We discuss how molecules form when CO and O 2 containing ices are exposed to thermal hydrogen atoms under fully controlled experimental conditions. Surface formation schemes for interstellar relevant species, such as solid methanol, water, and carbon dioxide are investigated and chemical links between molecular species in space are discussed.

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EXPERIMENTAL STUDY OF CO ₂ FORMATION BY SURFACE REACTIONS OF NON-ENERGETIC OH RADICALS WITH CO MOLECULES

Cited by 108 publications

References 42 publications

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects

THESPITZERICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS

Surface formation routes of interstellar molecules: hydrogenation reactions in simple ices

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EXPERIMENTAL STUDY OF CO 2 FORMATION BY SURFACE REACTIONS OF NON-ENERGETIC OH RADICALS WITH CO MOLECULES

Cited by 108 publications

References 42 publications

Solid CO2in low-mass young stellar objects

Solid CO2in low-mass young stellar objects

THESPITZERICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS

Surface formation routes of interstellar molecules: hydrogenation reactions in simple ices

Contact Info

Product

Resources

About

EXPERIMENTAL STUDY OF CO ₂ FORMATION BY SURFACE REACTIONS OF NON-ENERGETIC OH RADICALS WITH CO MOLECULES

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects