Formation of Carbon Dioxide by Surface Reactions on Ices in the Interstellar Medium

Roser, J. E.; Vidali, Gianfranco; Manicó, Giulio; Pirronello, V.

doi:10.1086/321732

Cited by 119 publications

(124 citation statements)

References 14 publications

Supporting

Mentioning

121

Contrasting

Order By: Relevance

“…Recently, Goumans & Andersson (2010) used harmonic quantum transition state theory to prove that, while quantum mechanical tunneling through the activation barrier increases the classical reaction rate for reaction 1 at low temperatures (10−20 K), the onset of tunneling is at temperatures that are too low for the reaction to efficiently contribute to CO 2 formation in quiescent cold regions. Reaction 1 has been experimentally investigated by temperatureprogramed desorption experiments using thermal O atoms below 160 K (Roser et al 2001) and by energetic O atoms (Madzunkov et al 2006). In the first case, reaction 1 was found to proceed only in water pores under a water ice cap and upon heating, while in the second case the energetic O atoms allowed the reaction to proceed.…”

Section: Introductionmentioning

confidence: 99%

Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

View full text Add to dashboard Cite

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 .

show abstract

Section: Introductionmentioning

confidence: 99%

Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

View full text Add to dashboard Cite

show abstract

“…If this selective fractionation remains unaltered by the processes of adsorption and desorption, then the 12 C/ 13 C ratio in various molecules could be used to distinguish between formation from CO on cold grains and gas-phase formation. Therefore Charnley et al (2004) propose that the 12 C/ 13 C ratio of hot-core methanol A&A 533, A24 (2011) should be compared to the corresponding isotopic ratio in CO 2 ices, since CO on cold grains has been shown to react also with atomic oxygen to form solid CO 2 (Roser et al 2001). Ices are not observed towards "regular" hot cores, but some embedded young stellar objects (YSOs), being at an earlier stage of evolution and harbouring ices in their envelopes, show characteristics implying a small hot core closest to the central object.…”

Section: Introductionmentioning

confidence: 99%

Observational tests of interstellar methanol formation

Wirström

Geppert

Hjalmarson

et al. 2011

A&A

View full text Add to dashboard Cite

Context. It has been established that the classical gas-phase production of interstellar methanol (CH 3 OH) cannot explain observed abundances. Instead it is now generally thought that the main formation path has to be by successive hydrogenation of solid CO on interstellar grain surfaces. Aims. While theoretical models and laboratory experiments show that methanol is efficiently formed from CO on cold grains, our aim is to test this scenario by astronomical observations of gas associated with young stellar objects (YSOs). Methods. We have observed the rotational transition quartets J = 2 K -1 K of 12 CH 3 OH and 13 CH 3 OH at 96.7 and 94.4 GHz, respectively, towards a sample of massive YSOs in different stages of evolution. In addition, the J = 1−0 transitions of 12 C 18 O and 13 C 18 O were observed towards some of these sources. We use the 12 C/ 13 C ratio to discriminate between gas-phase and grain surface origin: If methanol is formed from CO on grains, the ratios should be similar in CH 3 OH and CO. If not, the ratio should be higher in CH 3 OH due to 13 C fractionation in cold CO gas. We also estimate the abundance ratios between the nuclear spin types of methanol (E and A). If methanol is formed on grains, this ratio is likely to have been thermalized at the low physical temperature of the grain, and therefore show a relative over-abundance of A-methanol. Results. We show that the 12 C/ 13 C isotopic ratio is very similar in gas-phase CH 3 OH and C 18 O, on the spatial scale of about 40 , towards four YSOs. For two of our sources we find an overabundance of A-methanol as compared to E-methanol, corresponding to nuclear spin temperatures of 10 and 16 K. For the remaining five sources, the methanol E/A ratio is less than unity. Conclusions. While the 12 C/ 13 C ratio test is consistent with methanol formation from hydrogenation of CO on grain surfaces, the result of the E/A ratio test is inconclusive.

show abstract

“…Of the major ice species in our model (H 2 O, CO, CO 2 ), CO 2 has proven to be the most difficult to produce on surfaces via such processes (e.g. Ruffle & Herbst 2001). We have adopted an activation energy E A = 290 K, as measured by Roser et al (2001), for the important CO 2 (s) formation reaction between CO(s) and O(s) (Nummelin et al 2001).…”

Section: Chemical Model and Modificationsmentioning

confidence: 99%

“…Ruffle & Herbst 2001). We have adopted an activation energy E A = 290 K, as measured by Roser et al (2001), for the important CO 2 (s) formation reaction between CO(s) and O(s) (Nummelin et al 2001). Following the approach of Ruffle & Herbst (2001), we also consider a decreased activation energy E A of 130 K (see, for example, Grim & D'Hendecourt 1986;Fournier et al 1979;Tielens & Hagen 1982).…”

Section: Chemical Model and Modificationsmentioning

confidence: 99%

See 1 more Smart Citation

Beyond the pseudo-time-dependent approach: chemical models of dense core precursors

Hassel¹,

Herbst

Bergin

2010

A&A

View full text Add to dashboard Cite

Context. Chemical models of dense cloud cores often utilize the so-called pseudo-time-dependent approximation, in which the physical conditions are held fixed and uniform as the chemistry occurs. In this approximation, the initial abundances chosen, which are totally atomic in nature except for molecular hydrogen, are artificial. A more detailed approach to the chemistry of dense cold cores should include the physical evolution during their early stages of formation. Aims. Our major goal is to investigate the initial synthesis of molecular ices and gas-phase molecules as cold molecular gas begins to form behind a shock in the diffuse interstellar medium. The abundances calculated as the conditions evolve can then be utilized as reasonable initial conditions for a theory of the chemistry of dense cores. Methods. Hydrodynamic shock-wave simulations of the early stages of cold core formation are used to determine the time-dependent physical conditions for a gas-grain chemical network. We follow the cold post-shock molecular evolution of ices and gas-phase molecules as the visual extinction increases with time to A V ≈ 3. (Note that instead of an equal sign, the approximately equal sign should remain.) At higher extinction, self-gravity becomes important. Results. As the newly condensed gas enters its cool post-shock phase, a large amount of CO is produced in the gas. As the CO forms, water ice is produced on grains, while accretion of CO produces CO ice. The production of CO 2 ice from CO occurs via several surface mechanisms, while the production of CH 4 ice is slowed by gas-phase conversion of C into CO.

show abstract

Formation of Carbon Dioxide by Surface Reactions on Ices in the Interstellar Medium

Cited by 119 publications

References 14 publications

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects

Observational tests of interstellar methanol formation

Beyond the pseudo-time-dependent approach: chemical models of dense core precursors

Contact Info

Product

Resources

About

Formation of Carbon Dioxide by Surface Reactions on Ices in the Interstellar Medium

Cited by 119 publications

References 14 publications

Solid CO2in low-mass young stellar objects

Solid CO2in low-mass young stellar objects

Observational tests of interstellar methanol formation

Beyond the pseudo-time-dependent approach: chemical models of dense core precursors

Contact Info

Product

Resources

About

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects