Deuterium fractionation on interstellar grains studied with the direct master equation approach

Stantcheva, Tatiana; Herbst, Eric

doi:10.1046/j.1365-8711.2003.06368.x

Cited by 53 publications

(67 citation statements)

References 12 publications

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“…We included the major gaseous D-exchange reactions of the UMIST database (McElroy et al 2013), the major surface reactions identified by Stantcheva & Herbst (2003), and gas-phase reactions related to HDO using the approach of Aikawa et al (2012). The initial chemical abundances were adopted from Garrod et al (2007), and include the initial abundance [HD] = 1.5 × 10 −5 × [H 2 ] (Osamura et al 2005).…”

Section: Chemical Modeling Of Abundancementioning

confidence: 99%

Detection of a dense clump in a filament interacting with W51e2

Mookerjea

Vastel

Hassel

et al. 2014

A&A

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In the framework of the Herschel/PRISMAS guaranteed time key program, the line of sight to the distant ultracompact H ii region W51e2 has been observed using several selected molecular species. Most of the detected absorption features are not associated with the background high-mass star-forming region and probe the diffuse matter along the line of sight. We present here the detection of an additional narrow absorption feature at ∼70 km s −1 in the observed spectra of HDO, NH 3 and C 3 . The 70 km s −1 feature is not uniquely identifiable with the dynamic components (the main cloud and the large-scale foreground filament) so-far identified toward this region. The narrow absorption feature is similar to the one found toward low-mass protostars, which is characteristic of the presence of a cold external envelope. The far-infrared spectroscopic data were combined with existing ground-based observations of 12 CO, 13 CO, CCH, CN, and C 3 H 2 to characterize the 70 km s −1 component. Using a non-LTE analysis of multiple transitions of NH 3 and CN, we estimated the density (n(H 2 ) ∼ (1-5) × 10 5 cm −3 ) and temperature (10-30 K) for this narrow feature. We used a gasgrain warm-up based chemical model with physical parameters derived from the NH 3 data to explain the observed abundances of the different chemical species. We propose that the 70 km s −1 narrow feature arises in a dense and cold clump that probably undergoes collapse to form a low-mass protostar, formed on the trailing side of the high-velocity filament, which is thought to be interacting with the W51 main cloud. While the fortuitous coincidence of the dense clump along the line of sight with the continuum-bright W51e2 compact H ii region has contributed to its nondetection in the continuum images, this same attribute makes it an appropriate source for absorption studies and in particular for ice studies of star-forming regions.

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Section: Chemical Modeling Of Abundancementioning

confidence: 99%

Detection of a dense clump in a filament interacting with W51e2

Mookerjea

Vastel

Hassel

et al. 2014

A&A

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“…Therefore, it is not suitable for incorporation in codes that include complex networks of grain-surface reactions. In addition to the master equation method, a Monte Carlo method was proposed by Article published by EDP Sciences Tielens & Hagen (1982) and applied to interstellar modelling by Charnley (2001), Caselli et al (2002), and Stantcheva & Herbst (2003). Cuppen & Herbst (2005) developed random walk models for molecular hydrogen formation on grains that take into account the effect of surface roughness on the diffusion and reaction rates.…”

Section: Introductionmentioning

confidence: 99%

Incorporation of stochastic chemistry on dust grains in the Meudon PDR code using moment equations

Petit¹,

Barzel

Biham

et al. 2009

A&A

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Context. Unlike gas-phase reactions, chemical reactions taking place on interstellar dust grain surfaces cannot always be modeled by rate equations. Because of the small grain sizes and low flux, these reactions may exhibit large fluctuations and thus require stochastic methods such as the moment equations. Aims. We evaluate the formation rates of H 2 , HD, and D 2 molecules on dust grain surfaces and their abundances in the gas phase under interstellar conditions. Methods. We incorporate the moment equations into the Meudon PDR code and compare the results with those obtained from the rate equations. Results. We find that within the experimental constraints on the energy barriers for both diffusion and desorption and the density of adsorption sites on the grain surface, H 2 , HD and D 2 molecules can be formed efficiently on dust grains. Conclusions. In a wide range of conditions, the moment equation results agree with those obtained from the rate equations. However, for a range of relatively high grain temperatures, there are significant deviations: the rate equations fail, while the moment equations provide accurate results. The incorporation of the moment equations into the PDR code can be extended to other reactions taking place on grain surfaces.

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“…Presently published grain chemistry models predict an HDO fractionation of about 40% (i.e. almost all the deuterium would be locked in HDO) if deuterated water forms on the grain surfaces at the same time as formaldehyde and methanol (Caselli et al 2002;Stantcheva & Herbst 2003).…”

Section: Introductionmentioning

confidence: 99%

Search for solid HDO in low-mass protostars

Parise

Simon

Caux

et al. 2003

A&A

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Abstract. We present ground-based 2.1 to 4.2 µm observations of four low-mass protostars. We searched for the 4.1 µm OD stretch band, characteristic of solid HDO in grain mantles. We did not detect solid HDO in any of the four sources, but we derive 3σ upper limits from 0.5% to 2% for the HDO/H 2 O ratio depending on the source. These ratios provide strong constraints to solid-state deuteration models when compared to deuterium fractionation values observed in the gas phase. We discuss various scenarios that could lead to such a low water deuteration compared to the high formaldehyde and methanol deuteration observed in the gas-phase.

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Deuterium fractionation on interstellar grains studied with the direct master equation approach

Cited by 53 publications

References 12 publications

Detection of a dense clump in a filament interacting with W51e2

Detection of a dense clump in a filament interacting with W51e2

Incorporation of stochastic chemistry on dust grains in the Meudon PDR code using moment equations

Search for solid HDO in low-mass protostars

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