ON THE FORMATION OF CO<sub>2</sub>AND OTHER INTERSTELLAR ICES

Garrod, R. T.; Pauly, Tyler

doi:10.1088/0004-637x/735/1/15

Cited by 256 publications

(403 citation statements)

References 51 publications

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“…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). This is also recently confirmed by Garrod & Pauly (2011) in their three-phase (gas/surface/mantle) astrochemical model in which formation of solid CO 2 , as well as other species, is investigated. Thus, a combination of observations, models, and laboratory experiments indicates that CO 2 can be formed through non-energetic induced surface reactions in a polar environment already in a quiescent molecular cloud phase.…”

Section: Introductionsupporting

confidence: 55%

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: Introductionsupporting

confidence: 55%

Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

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“…-the O/H ratio, very probably the most important parameter; -the grain temperature: the higher it is the shorter is the H residence time on the grain and thus the probability of OH formation; -H and O diffusion on the surface: since only the first one is usually considered in models (e.g., Garrod & Pauly 2011), the CO + O contribution is, in our opinion, underestimated.…”

Section: Astrophysical Conclusionmentioning

confidence: 92%

CO₂formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel

Minissale

Congiu

Manicó

et al. 2013

A&A

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Context. The formation of carbon dioxide in quiescent regions of molecular clouds has not yet been fully understood, even though CO 2 is one of the most abundant species in interstellar ices. Aims. CO 2 formation is studied via oxidation of CO molecules on cold surfaces under conditions close to those encountered in quiescent molecular clouds. Methods. Carbon monoxide and oxygen atoms are codeposited using two differentially pumped beam lines on two different surfaces (amorphous water ice or oxydized graphite) held at given temperatures between 10 and 60 K. The products are probed via mass spectroscopy by using the temperature-programmed desorption technique. Results. We show that the reaction CO + O can form carbon dioxide in solid phase with an efficiency that depends on the temperature of the surface. The activation barrier for the reaction, based on modelling results, is estimated to be in the range of 780−475 K/k b . Our model also allows us to distinguish the mechanisms (Eley Rideal or Langmuir-Hinshelwood) at play in different temperature regimes. Our results suggest that competition between CO 2 formation via CO + O and other surface reactions of O is a key factor in the yields of CO 2 obtained experimentally. Conclusions. CO 2 can be formed by the CO + O reaction on cold surfaces via processes that mimic carbon dioxide formation in the interstellar medium. Astrophysically, the presence of CO 2 in quiescent molecular clouds could be explained by the reaction CO + O occurring on interstellar dust grains.

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“…The three-phase model used here is described in detail by Garrod & Pauly (2011), and is based on the approach of Hasegawa & Herbst (1993). In contrast to both of those methods, MAGICKAL simulates an active ice-mantle chemistry in addition to that occurring in the surface layer of the ice or on the dust-grain surface.…”

Section: Three-phase Modelmentioning

confidence: 99%

A Three-Phase Chemical Model of Hot Cores: The Formation of Glycine

Garrod

2013

ApJ

412

700

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A new chemical model is presented that simulates fully coupled gas-phase, grain-surface, and bulk-ice chemistry in hot cores. Glycine (NH 2 CH 2 COOH), the simplest amino acid, and related molecules such as glycinal, propionic acid, and propanal, are included in the chemical network. Glycine is found to form in moderate abundance within and upon dust-grain ices via three radical-addition mechanisms, with no single mechanism strongly dominant. Glycine production in the ice occurs over temperatures ∼40-120 K. Peak gas-phase glycine fractional abundances lie in the range 8 × 10 −11 -8 × 10 −9 , occurring at ∼200 K, the evaporation temperature of glycine. A gas-phase mechanism for glycine production is tested and found insignificant, even under optimal conditions. A new spectroscopic radiative-transfer model is used, allowing the translation and comparison of the chemical-model results with observations of specific sources. Comparison with the nearby hot-core source NGC 6334 IRS1 shows excellent agreement with integrated line intensities of observed species, including methyl formate. The results for glycine are consistent with the current lack of a detection of this molecule toward other sources; the high evaporation temperature of glycine renders the emission region extremely compact. Glycine detection with ALMA is predicted to be highly plausible, for bright, nearby sources with narrow emission lines. Photodissociation of water and subsequent hydrogen abstraction from organic molecules by OH, and NH 2 , are crucial to the buildup of complex organic species in the ice. The inclusion of alternative branches within the network of radical-addition reactions appears important to the abundances of hot-core molecules; less favorable branching ratios may remedy the anomalously high abundance of glycolaldehyde predicted by this and previous models.

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ON THE FORMATION OF CO₂AND OTHER INTERSTELLAR ICES

Cited by 256 publications

References 51 publications

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects

CO₂formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel

A Three-Phase Chemical Model of Hot Cores: The Formation of Glycine

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ON THE FORMATION OF CO2AND OTHER INTERSTELLAR ICES

Cited by 256 publications

References 51 publications

Solid CO2in low-mass young stellar objects

Solid CO2in low-mass young stellar objects

CO2formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel

A Three-Phase Chemical Model of Hot Cores: The Formation of Glycine

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ON THE FORMATION OF CO₂AND OTHER INTERSTELLAR ICES

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects

CO₂formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel