CO<sub>2</sub>FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

Noble, J. A.; Dulieu, F.; Congiu, E.; Fraser, H. J.

doi:10.1088/0004-637x/735/2/121

Cited by 94 publications

(123 citation statements)

References 53 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: 52%

“…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: 52%

Section: Introductionmentioning

confidence: 99%

Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

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“…Garrod et al (2007) have previously proposed a formula in their models that can be used to describe the chemical desorption (or reactive desorption). They derived the probability of A24, page 4 of 6 Bergeron et al (2008); (c) Al-Halabi & van Dishoeck (2007), Amiaud et al (2007); (d) Pirronello et al (1997); (e) Amiaud et al (2006) for low coverage; ( f ) Minissale et al (2015); (g) Dulieu et al (2013); (h) Speedy et al (1996), Fraser et al (2001 energy derived of 5800 K with pre-factor of 10 15 s −1 here corrected to have a pre-factor of 10 12 s −1 ; (i) Noble et al (2012a); ( (2)) that include division between the degree of freedom and the fraction of kinetic energy after bounce ( is mass dependent). In red we show the equal share of energy and the constant value of .…”

Section: Theoretical Estimate Of the Desorption Efficiencymentioning

confidence: 99%

Dust as interstellar catalyst

Minissale

Dulieu

Cazaux

et al. 2015

A&A

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Context. The presence of dust in the interstellar medium has profound consequences on the chemical composition of regions where stars are forming. Recent observations show that many species formed onto dust are populating the gas phase, especially in cold environments where UV-and cosmic-ray-induced photons do not account for such processes. Aims. The aim of this paper is to understand and quantify the process that releases solid species into the gas phase, the so-called chemical desorption process, so that an explicit formula can be derived that can be included in astrochemical models. Methods. We present a collection of experimental results of more than ten reactive systems. For each reaction, different substrates such as oxidized graphite and compact amorphous water ice were used. We derived a formula for reproducing the efficiencies of the chemical desorption process that considers the equipartition of the energy of newly formed products, followed by classical bounce on the surface. In part II of this study we extend these results to astrophysical conditions. Results. The equipartition of energy correctly describes the chemical desorption process on bare surfaces. On icy surfaces, the chemical desorption process is much less efficient, and a better description of the interaction with the surface is still needed. Conclusions. We show that the mechanism that directly transforms solid species into gas phase species is efficient for many reactions.

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“…In recent experimental studies it has clearly been shown that reaction 1 leads to CO 2 formation, although no consistent results were obtained concerning the activation barrier: little or barrierless in Oba et al (2011) and "high" (400 K) in Noble et al (2011). Reaction 2 has been studied theoretically (Talbi et al 2006;Goumans et al 2008), and those studies suggest there is a high activation barrier (2500−3000 K).…”

Section: Introductionmentioning

confidence: 98%

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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CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

Cited by 94 publications

References 53 publications

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects

Dust as interstellar catalyst

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

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CO2FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

Cited by 94 publications

References 53 publications

Solid CO2in low-mass young stellar objects

Solid CO2in low-mass young stellar objects

Dust as interstellar catalyst

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

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Resources

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CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

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