Interstellar oxygen chemistry

Viti, S.; Roueff, E.; Hartquist, T. W.; Forêts, G. Pineau des; Williams, D. A.

doi:10.1051/0004-6361:20010246

Cited by 55 publications

(66 citation statements)

References 35 publications

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“…Our model includes surface reactions and desorption mechanisms for all species, and so is more "complete" than previous accretion models, such as those of Bergin et al (2000) and Viti et al (2001). However, our gas-grain model is at its weakest at late times since the gas-phase abundances are strongly affected by the uncertain desorption rates adopted.…”

Section: Discussionmentioning

confidence: 99%

“…Two such approaches are those of Viti et al (2001) and Charnley et al (2001). Viti et al (2001) have constructed many models with gasphase chemistry and with accretion to study a variety of physical conditions.…”

Section: Discussionmentioning

confidence: 99%

“…The role of shocks has been studied to a greater degree by Charnley et al (2001). The role of accretion has been explored by Viti et al (2001), who considered cyclic gas-phase models in which CO and N 2 are allowed to accrete onto grains and return to the gas-phase when other heavy molecules remain on the grains. They also suggested that the high ionisation phase of bistable models provides a natural explanation for the low abundance of oxygen.…”

Section: Introductionmentioning

confidence: 99%

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The abundance of gaseous H$_{\mathsf 2}$O and O$_{\mathsf 2}$ in cores of dense interstellar clouds

Roberts

Herbst

2002

A&A

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Abstract.We have used chemical models that include both gas-phase and grain-surface processes to try to understand the low water and molecular oxygen abundances inferred from SWAS observations towards dense molecular clouds. The models represent an improvement over pure gas-phase chemistries in that they are more realistic, and they are largely successful at reproducing the low O 2 abundances. For cold clouds, such as TMC-1 and L134N, the limits on the H 2 O abundance are met by the models only after relatively long periods of accretion (10 6 -10 7 yr), but we show that ground-based observations of these clouds do not necessarily contradict these ages, especially for L134N. If the upper limits on the H 2 O abundance were to be revised downwards, however, or if water were to be observed in the cold clouds at the same level as in some star-forming regions, then even heavier depletions would be required. For this reason, the low H 2 O abundance observed by SWAS in ρ Oph cannot be reproduced by the models without calculating unphysically low abundances of CO.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The abundance of gaseous H$_{\mathsf 2}$O and O$_{\mathsf 2}$ in cores of dense interstellar clouds

Roberts

Herbst

2002

A&A

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“…From a chemical modeling point of view, pure gas-phase chemical models can explain the observed upper limits for clouds younger than 10 5 yr (Wakelam et al 2006a). Viti et al (2001) explored the possibility that chemical models can display bistabilities (Le Bourlot et al 1993). In the parameter space where bistability exists, one of the solutions is characterized by a very low abundance of O 2 .…”

Section: Introductionmentioning

confidence: 99%

Oxygen depletion in dense molecular clouds: a clue to a low O₂abundance?

Hincelin

Wakelam

Hersant

et al. 2011

A&A

144

154

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Context. Dark cloud chemical models usually predict large amounts of O 2 , often above observational limits. Aims. We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods. We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the sensitivity of the molecular oxygen abundance to the oxygen elemental abundance. We use the rate coefficient for the reaction O + OH at 10 K recommended by the KIDA (KInetic Database for Astrochemistry) experts. Results. The updates of rate coefficients and branching ratios of the reactions of our gas-phase chemical network, especially N + CN and H + 3 + O, have changed the model sensitivity to the oxygen elemental abundance. In addition, the gas-phase abundances calculated with our gas-grain model are less sensitive to the elemental C/O ratio than those computed with a pure gas-phase model. The grain surface chemistry plays the role of a buffer absorbing most of the extra carbon. Finally, to reproduce the low abundance of molecular oxygen observed in dark clouds at all times, we need an oxygen elemental abundance smaller than 1.6 × 10 −4 . Conclusions. The chemistry of molecular oxygen in dense clouds is quite sensitive to model parameters that are not necessarily well constrained. That O 2 abundance may be sensitive to nitrogen chemistry is an indication of the complexity of interstellar chemistry.

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“…Indeed, such models replicate the complex organic chemistry seen in TMC-1 best (Wakelam et al 2006). Other solutions to the O 2 /H 2 O problems involve shocks, turbulence, bistability, and grain chemistry in some manner ( Bergin et al 2000;Charnley et al 2001;Spaans & van Dishoeck 2001;Viti et al 2001;Willacy et al 2002;Roberts & Herbst 2002). In the most recent gas-grain model study of cold cores, Garrod et al (2007) show that small abundances of O 2 and H 2 O can be achieved over a significant range of times even if standard O-rich abundances are utilized.…”

Section: Introductionmentioning

confidence: 96%

New Theoretical Results Concerning the Interstellar Abundance of Molecular Oxygen

Quan

Herbst

Millar

et al. 2008

ApJ

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The low abundance of molecular oxygen in cold cores of interstellar clouds poses a continuing problem to modelers of the chemistry of these regions. In chemical models O 2 is formed principally by the reaction between O and OH, which has been studied experimentally down to 39 K. It remains possible that the rate coefficient of this reaction at 10 K is considerably less than its measured value at 39 K, which might inhibit the production of O 2 and possibly bring theory and observation closer together over a wider range of times. Two theoretical determinations of the rate coefficient for the O þ OH reaction at temperatures down to 10 K have been undertaken recently; both results show that the rate coefficient is indeed lower at 10 K than at 39 K, although they differ in the magnitude of the decrease. Here we show, using gas-phase models, how the calculated interstellar O 2 abundance in cold cores is affected by a decrease in the rate coefficient. We also consider its effect on other species. Our major finding is that for standard O-rich abundances, the calculated abundance of O 2 in cold cores is sufficiently low to explain observations only at early times regardless of the value of k 1 in the range investigated here. For C-rich abundances, on the other hand, late-time solutions can also be possible.

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Interstellar oxygen chemistry

Cited by 55 publications

References 35 publications

The abundance of gaseous H$_{\mathsf 2}$O and O$_{\mathsf 2}$ in cores of dense interstellar clouds

The abundance of gaseous H$_{\mathsf 2}$O and O$_{\mathsf 2}$ in cores of dense interstellar clouds

Oxygen depletion in dense molecular clouds: a clue to a low O₂abundance?

New Theoretical Results Concerning the Interstellar Abundance of Molecular Oxygen

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Interstellar oxygen chemistry

Cited by 55 publications

References 35 publications

The abundance of gaseous H$_{\mathsf 2}$O and O$_{\mathsf 2}$ in cores of dense interstellar clouds

The abundance of gaseous H$_{\mathsf 2}$O and O$_{\mathsf 2}$ in cores of dense interstellar clouds

Oxygen depletion in dense molecular clouds: a clue to a low O2abundance?

New Theoretical Results Concerning the Interstellar Abundance of Molecular Oxygen

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Oxygen depletion in dense molecular clouds: a clue to a low O₂abundance?