Cosmic dust and our origins

Greenberg, J. Mayo

doi:10.1016/s0039-6028(01)01555-2

Cited by 107 publications

(127 citation statements)

References 47 publications

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“…Amorphous silicate is an appropriate mimic of interstellar dust grains, composed of siliceous and carbonaceous material (Greenberg 2002). In molecular clouds these grains are covered in an ice mantle, the largest component of which is H 2 O, at abundances of up to 100 ML (Williams & Herbst 2002).…”

Section: Methodsmentioning

confidence: 99%

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

Noble¹,

Dulieu²,

Congiu³

et al. 2011

ApJ

114

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The formation of CO 2 in quiescent regions of molecular clouds is not yet fully understood, despite CO 2 having an abundance of around 10%-34% H 2 O. We present a study of the formation of CO 2 via the nonenergetic route CO + OH on nonporous H 2 O and amorphous silicate surfaces. Our results are in the form of temperature-programmed desorption spectra of CO 2 produced via two experimental routes: O 2 + CO + H and O 3 + CO + H. The maximum yield of CO 2 is around 8% with respect to the starting quantity of CO, suggesting a barrier to CO + OH. The rate of reaction, based on modeling results, is 24 times slower than O 2 + H. Our model suggests that competition between CO 2 formation via CO + OH and other surface reactions of OH is a key factor in the low yields of CO 2 obtained experimentally, with relative reaction rates ofAstrophysically, the presence of CO 2 in low A V regions of molecular clouds could be explained by the reaction CO + OH occurring concurrently with the formation of H 2 O via the route OH + H.

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Section: Methodsmentioning

confidence: 99%

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

Noble¹,

Dulieu²,

Congiu³

et al. 2011

ApJ

114

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“…The chemical nature of dust grains in the ISM has not been characterized well, but astronomical data show that they are principally composed of silicate and carbonaceous material. In diffuse (low density) clouds, the dust grains are bare, but in dark (dense) clouds the grains are covered with an icy mantle, mainly composed of amorphous solid water with added CO, CO 2 , methanol, and other molecules (Gibb et al 2000;Greenberg 2002). Since the formation of H 2 molecules (in the ISM) from H atoms is assumed to be preceded by the sticking of hydrogen atoms on dust grains, many theoretical studies devoted to this topic have been developed (Hollenbach & Salpeter 1971;Burke & Hollenbach 1983;Leitch-Devlin & Williams 1985).…”

Section: Introductionmentioning

confidence: 99%

Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions

Chaabouni

Bergeron

Baouche

et al. 2012

A&A

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Context.Sticking of H and D atoms on interstellar dust grains is the first step in molecular hydrogen formation, which is a key reaction in the interstellar medium. Isotopic properties of the sticking can have an incidence on the observed HD molecule. Aims. After studying the sticking coefficients of H 2 and D 2 molecules on amorphous silicate surfaces experimentally and theoretically, we extrapolate the results to the sticking coefficient of atoms and propose a formulae that gives the sticking coefficients of H and D on both silicates and icy dust grains. Methods. In our experiments, we used the King and Wells method for measuring the sticking coefficients of H 2 and D 2 molecules on a silicate surface held at 10 K. It consists of measuring with a QMS (quadrupole mass spectrometer) the signals of H 2 and D 2 molecules reflected by the surface during the exposure of the sample to the molecular beam at a temperature ranging from 20 K to 340 K. We tested the efficiency of a physical model, developed previously for sticking on water-ice surfaces. We applied this model to our experimental results for the sticking coefficients of H 2 and D 2 molecules on a silicate surface and estimated the sticking coefficient of atoms by a single measurement of atomic recombination and propose an extrapolation. Results. Sticking of H, D, HD, H 2 , and D 2 on silicates grains behaves the same as on icy dust grains. The sticking decreases with the gas temperature, and is dependent on the mass of the impactor. The sticking coefficient for both surfaces and impactors can be modeled by an analytical formulae S (T ) = S 0 (1 + βT/T 0 )/(1 + T/T 0 ) β , which describes both the experiments and the thermal distribution expected in an astrophysical context. The parameters S 0 and T 0 are summarized in a table. Conclusions. Previous estimates for the sticking coefficient of H atoms are close to the new estimation; however, we find that, when isotopic effects are taken into account, the sticking coefficient variations can be as much as a factor of 2 at T = 100 K.

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“…Complex refractory organic matter accompanied by D-and/or 15 N-enrichment could have formed as a result of UV irradiation on ice grains condensed from gas molecules in cold molecular clouds (Bernstein et al, 1999;Greenberg, 2002), and in the early solar nebula (e.g., Schutte et al, 1992;Allamandola et al, 1988;Greenberg et al, 1995;Ciesla and Sandford, 2012). Three processes have mainly been discussed to explain such large isotopic enrichments of D and 15 N observed in the organic matter of meteorites: 1) ion-molecule reactions in cold molecular cloud and in the outer protoplanetary disk, 2) grainsurface reactions in cold molecular clouds, and 3) selfshielding in molecular clouds and in the outer protoplanetary disk.…”

Section: Formation Processes For D-and 15 N-enrichment In the Organicmentioning

confidence: 99%

“…Organic matter with D-rich isotopic compositions could be produced via the grain-surface reactions in cold molecular cloud (Fig. 9) and the ice grains would be changed to organic matter by UV irradiation (e.g., Bernstein et al, 1999;Greenberg, 2002;Ciesla and Sandford, 2012). D-enrichment produced by grain-surface reaction is predicted to be significantly larger (e.g., ~10…”

Section: Formation Processes For D-and 15 N-enrichment In the Organicmentioning

confidence: 99%

“…Organic matter could have been formed by ultraviolet (UV) irradiation onto ice grains in the molecular cloud (Greenberg, 2002) and in the outer disk of the early solar nebula (Ciesla and Sandford, 2012). Saito and Kimura (2009) suggested that nanometer sized organic globules could be formed by irradiation of plasma particles such as protons and He + around evolved stars.…”

Section: Morphology Of the Isotopically Anomalous Organic Mattermentioning

confidence: 99%

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