Molecular Hydrogen formation on grain surfaces

Cazaux, S.; Caselli, P.; Tielens, A. G. G. M.; Bourlot, J. Le; Walmsley, M.

doi:10.1088/1742-6596/6/1/016

Cited by 38 publications

(45 citation statements)

References 27 publications

(31 reference statements)

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“…The quantities H 2 and S (T ) can be calculated from models or measured from laboratory experiments (e.g. Hollenbach & McKee 1979;Cazaux & Tielens 2002, 2004Cazaux et al 2005), while Σ gr can be constrained approximately from the level of dust extinction in the UV (Draine 2003(Draine , 2011, and references therein). However, a more common approach is to constrain the entirety of R gr via observations of C i, C ii, H i, and H 2 column densities.…”

Section: The Atomic To Molecular Transitionmentioning

confidence: 99%

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

2014

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Star formation lies at the center of a web of processes that drive cosmic evolution: generation of radiant energy, synthesis of elements, formation of planets, and development of life. Decades of observations have yielded a variety of empirical rules about how it operates, but at present we have no comprehensive, quantitative theory. In this review I discuss the current state of the field of star formation, focusing on three central questions: what controls the rate at which gas in a galaxy converts to stars? What determines how those stars are clustered, and what fraction of the stellar population ends up in gravitationally-bound structures? What determines the stellar initial mass function, and does it vary with star-forming environment? I use these three question as a lens to introduce the basics of star formation, beginning with a review of the observational phenomenology and the basic physical processes. I then review the status of current theories that attempt to solve each of the three problems, pointing out links between them and opportunities for theoretical and numerical work that crosses the scale between them. I conclude with a discussion of prospects for theoretical progress in the coming years.

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Section: The Atomic To Molecular Transitionmentioning

confidence: 99%

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

2014

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“…Second, one can consider H 2 formation on surfaces that strongly support bound binding sites, known as chemisorption. The first attempt to use chemisorption to produce H 2 under astronomical conditions was undertaken by Cazaux & Tielens (2002 and Cazaux et al (2005). These authors found that chemisorption extends the upper temperature limit for efficient H 2 formation considerably.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the technique can be used for rough and even amorphous surfaces by assigning different energy parameters to individual sites, and can simulate several mechanisms of surface reactions besides the diffusive (Langmuir-Hinshelwood) one, including the Eley-Rideal mechanism, in which a gas-phase species lands directly on an adsorbate, and reactions within the gaps of porous ices. The technique has been used to look at the development of ice mantles (Cuppen & Herbst 2007;Cuppen et al 2009) and probe details of H 2 formation (Cazaux et al 2005;Cuppen et al 2006;. Chakrabarti et al (2006) used a similar method that keeps track of each individual reactant and their movements and calculated the effective grain surface area involved in the formation of molecular hydrogen in interstellar clouds.…”

Section: Introductionmentioning

confidence: 99%

KINETIC MONTE CARLO STUDIES OF H₂FORMATION ON GRAIN SURFACES OVER A WIDE TEMPERATURE RANGE

Iqbal

Acharyya

Herbst

2012

ApJ

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We have used the continuous-time random-walk Monte Carlo technique to study the formation of H 2 from two hydrogen atoms on the surface of interstellar dust grains with both physisorption and chemisorption sites on olivine and carbonaceous material. In our standard approach, atoms must first enter the physisorption site before chemisorption can occur. We have considered hydrogen atom mobility due to both thermal hopping and quantum mechanical tunneling. The temperature range between 5 K and 825 K has been explored for different incoming H fluxes representative of interstellar environments with atomic hydrogen number density ranging between 0.1 cm −3 and 100 cm −3 and dust grain sizes ranging from 100 sites to 10 6 sites, the latter corresponding roughly to olivine grains of radius 0.2 μm. In addition, we have also considered rough surfaces with multiple binding sites. Tunneling is found to dominate the surface chemistry at low temperature, but as the temperature increases, the scenario changes. The inclusion of chemisorption sites can provide a meaningful efficiency for H 2 production up to temperatures as high as 700 K depending upon the depth of the chemisorption well. We found that over virtually the entire temperature range studied, the use of rate equations overestimates the H 2 formation rate to some extent. This overestimate is large at high temperatures, due to very low surface residence times. We have also considered models in which chemisorption sites are entered directly and diffusion proceeds only to other chemisorption sites.

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“…This sticking probability also depends on surface properties, such as porosity and distribution of surface chemi-and physisorption sites. Chemisorption requires formation of a chemical bond between a surface species and a grain, and such a species does not evaporate easily (e.g., Cazaux et al 2005).…”

Section: Gas-grain Interactionsmentioning

confidence: 99%

Chemical Evolution of a Protoplanetary Disk

Semenov

2011

Proc. IAU

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Abstract. In this paper we review recent progress in our understanding of the chemical evolution of protoplanetary disks. Current observational constraints and theoretical modeling on the chemical composition of gas and dust in these systems are presented. Strong variations of temperature, density, high-energy radiation intensities in these disks, both radially and vertically, result in a peculiar disk chemical structure, where a variety of processes are active. In hot, dilute and heavily irradiated atmosphere only the most photostable simple radicals and atoms and atomic ions exist, formed by gas-phase processes. Beneath the atmosphere a partly UVshielded, warm molecular layer is located, where high-energy radiation drives rich ion-molecule and radical-radical chemistry, both in the gas phase and on dust surfaces. In a cold, dense, dark disk midplane many molecules are frozen out, forming thick icy mantles where surface chemistry is active and where complex polyatomic (organic) species are synthesized. Dynamical processes affect disk chemical composition by enriching it in abundances of complex species produced via slow surface processes, which will become detectable with ALMA.

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Molecular Hydrogen formation on grain surfaces

Cited by 38 publications

References 27 publications

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

KINETIC MONTE CARLO STUDIES OF H₂FORMATION ON GRAIN SURFACES OVER A WIDE TEMPERATURE RANGE

Chemical Evolution of a Protoplanetary Disk

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Molecular Hydrogen formation on grain surfaces

Cited by 38 publications

References 27 publications

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function

KINETIC MONTE CARLO STUDIES OF H2FORMATION ON GRAIN SURFACES OVER A WIDE TEMPERATURE RANGE

Chemical Evolution of a Protoplanetary Disk

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KINETIC MONTE CARLO STUDIES OF H₂FORMATION ON GRAIN SURFACES OVER A WIDE TEMPERATURE RANGE