Molecular hydrogen formation on porous dust grains

Perets, Hagai B.; Biham, Ofer

doi:10.1111/j.1365-2966.2005.09803.x

Cited by 23 publications

(21 citation statements)

References 64 publications

(90 reference statements)

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“…However, with careful experimental design and the use of simulations to reproduce the conditions in the ISM, as performed by Katz et al (1999) and Biham and Lipshtat (2002), the efficiency of H 2 formation in the ISM can be obtained from experimental kinetic data. Further work by the Biham's group studied the effect of particle size (Lipshtat and Biham, 2005) and porosity (Perets and Biham, 2006) on H 2 formation in interstellar environments. Diffusion of H atoms was included in the simulations of the formation kinetics (Katz et al, 1999), revealing that the ratio of the energy barrier for H atom diffusion to the binding energy is considerably higher than the typically assumed value (∼ 0.3 ) for physisorbed atoms on single crystal surfaces (Bruch et al, 2007b).…”

Section: Silicate Surfacesmentioning

confidence: 99%

H 2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations

Wakelam

Bron

Cazaux

et al. 2017

Molecular Astrophysics

221

201

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a b s t r a c tMolecular hydrogen is the most abundant molecule in the universe. It is the first one to form and survive photo-dissociation in tenuous environments. Its formation involves catalytic reactions on the surface of interstellar grains. The micro-physics of the formation process has been investigated intensively in the last 20 years, in parallel of new astrophysical observational and modeling progresses. In the perspectives of the probable revolution brought by the future satellite JWST, this article has been written to present what we think we know about the H 2 formation in a variety of interstellar environments.

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Section: Silicate Surfacesmentioning

confidence: 99%

H 2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations

Wakelam

Bron

Cazaux

et al. 2017

Molecular Astrophysics

221

201

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“…It would indeed appear that a more complex surface model is required to explain the efficient formation of molecular hydrogen in diffuse clouds. The effect of porosity has been considered by Perets & Biham (2006) and found to be small. Recently, we showed that on a "rough" surface, with sites on which adsorbates can have different binding energies, molecular hydrogen can be formed efficiently over a wider range of temperature (Chang et al 2005;Cuppen et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Effective rate coefficients for molecular hydrogen formation in diffuse interstellar clouds

Chang¹,

Cuppen²,

Herbst

2006

A&A

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Aims. A method to determine effective rate coefficients for H 2 formation on grain surfaces is proposed based on the continuous-time, random-walk Monte Carlo simulation. Methods. Our Monte Carlo simulation is used to calculate the efficiency of molecular hydrogen formation via recombination of H atoms on flat and rough surfaces of olivine and amorphous carbon under a variety of diffuse cloud conditions. The results are then fitted to two types of rate laws to determine effective rate coefficients for use in rate equation treatments. These rate coefficients can be utilized in pure gas-phase models, where the rate of molecular formation is associated with a grain collision rate for H atoms multiplied by an efficiency factor, and in gas-grain models, where the actual diffusion of H atoms on a grain surface is considered. Results. The effective rate coefficients are tabulated as a function of incoming atomic hydrogen flux and surface temperature, over temperature ranges for which the surfaces show a reasonable efficiency of molecular hydrogen formation. For the flat surfaces studied, corrections to the standard rate treatment do not exceed a factor of three.

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“…To model the impact of the porous structures of interstellar grains, we introduce two types of sites: the non-porous, and the porous sites, following Perets & Biham (2006). The non-porous sites form a smooth surface that is perfectly regular, where particles interact directly with the gas phase.…”

Section: Porositymentioning

confidence: 99%

“…As previously discussed, the presence of pores creates traps for the molecules and atoms on the grain surfaces, leading to an enhancement of reactivity on the grains. GRAINOBLE includes pores, following the treatment of Perets & Biham (2006). The number and area of the pores are treated as parameters (Sect.…”

Section: B) Porosity Of the Grainsmentioning

confidence: 99%

Multilayer modeling of porous grain surface chemistry

Taquet

Ceccarelli

Kahane

2012

A&A

141

157

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Context. Mantles of iced water mixed with carbon monoxyde, formaldehyde, and methanol are formed during the so-called prestellar core phase. In addition, radicals are also thought to be formed on the grain surfaces, and to react to form complex organic molecules later on, during the so-called warm-up phase of the protostellar evolution. Aims. We aim to study the formation of the grain mantles during the prestellar core phase and the abundance of formaldehyde, methanol, and radicals trapped in them. Methods. We have developed a macrosopic statistic multilayer model that follows the formation of grain mantles with time and that includes two effects that may increase the number of radicals trapped in the mantles: i) during the mantle formation, only the surface layer is chemically active and not the entire bulk; and ii) the porous structure of grains allows the trapping reactive particles. The model considers a network of H, O, and CO forming neutral species such as water, CO, formaldehyde, and methanol, plus several radicals. We ran a large grid of models to study the impact of the mantle multilayer nature and grain porous structure. In addition, we explored how the uncertainty of other key parameters influences the mantle composition. Results. Our model predicts relatively high abundances of radicals, especially of HCO and CH 3 O (10 −9 −10 −7 ). In addition, the multilayer approach enables us to follow the chemical differentiation within the grain mantle, showing that the mantles are far from being uniform. For example, methanol is mostly present in the outer layers of the mantles, whereas CO and other reactive species are trapped in the inner layers. The overall mantle composition depends on the density and age of the prestellar core as well as on some microscopic parameters, such as the diffusion energy and the hydrogenation reactions activation energy. Comparison with observations allows us to constrain the value of the last two parameters (0.5-0.65 and 1500 K, respectively) and provide some indications on the physical conditions during the formation of the ices.

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Molecular hydrogen formation on porous dust grains

Cited by 23 publications

References 64 publications

H 2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations

H 2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations

Effective rate coefficients for molecular hydrogen formation in diffuse interstellar clouds

Multilayer modeling of porous grain surface chemistry

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