Molecular Hydrogen Formation on Astrophysically Relevant Surfaces

Katz, Nadav; Furman, Itay; Biham, Ofer; Pirronello, V.; Vidali, Gianfranco

doi:10.1086/307642

Cited by 324 publications

(516 citation statements)

References 21 publications

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“…While that can be the case, our data show that different functionals may play a significative role in changing the physisorption value, which imposes some caution when using DFT for computing very weak interactions in open-shell systems. The computed value of the kinetic barrier for H jump between physisorbed sites resulted in 4.1 kcal mol -1 (Table 3), much higher than the experimental datum reported by Katz et al 43 of only 0.57 kcal mol -1 . Goumans et al 21 computed a value of 1.6 kcal mol -1 while Kerkeni and Bromley 17 a range between 0.14 -4.8 kcal mol -1 as a function of the considered path on the heterogeneous cluster surface.…”

Section: Resultscontrasting

confidence: 56%

“…It can be shown that the E(T) is less than 0.05 kcal mol -1 (2 meV, 20 K) while RT is 0.02 kcal mol -1 (1 meV, 10 K) at 10 K and ten times higher at T = 100 K. Using data from Table 1 we arrive at our best estimate of Hd = 1.8 kcal mol -1 (900 K) at the experimental temperature of 10 K. The datum obtained from the experimental TPD measurements 43 is 318 K, three times smaller than our best estimate. Modeling studies described in the introduction section report data which are also higher than the experimental datum.…”

Section: Resultsmentioning

confidence: 76%

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Interstellar H adsorption and H₂formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

Navarro‐Ruiz

Sodupe

Ugliengo

et al. 2014

Phys. Chem. Chem. Phys.

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The physisorption/chemisorption of atomic hydrogen on a slab model of the Mg2SiO4 forsterite (010) surface mimicking the interstellar dust particle surface has been modeled using a quantum mechanical approach based on periodic B3LYP-D2* density functional calculations (DFT) combined with flexible polarized Gaussian type basis sets, which allows a balanced description of the hydrogen/surface interactions for both minima and attachment of H at the surface at 100 K, but prevents the same process to occur at 10 K.From this H-chemisorbed state, second hydrogen chemisorption mainly occurs on the neighboring Mg ion, thus forming a Mg-H surface group, giving rise to a surface species stabilized by favorable electrostatic interactions between the OH + /H -Mg pair. The formation of molecular hydrogen at the (010) forsterite surface adopting a LangmuirHinshelwood mechanism takes place either starting from two physisorbed H atoms with an almost negligible kinetic barrier through a spin-spin coupling driven reaction or from two chemisorbed H atoms with a barrier surmountable already at T higher than 10 K. We also suggest that a nanosized model of the interstellar dust built from a replica of the forsterite unit cell is able to adsorb half the energy released by the H2 formation by increasing its temperature by about 50 K which could then radiates in about 0.02 s.

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Section: Resultscontrasting

confidence: 56%

Section: Resultsmentioning

confidence: 76%

Interstellar H adsorption and H₂formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

Navarro‐Ruiz

Sodupe

Ugliengo

et al. 2014

Phys. Chem. Chem. Phys.

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“…2e). Here, we consider nH = 2 × 10 4 cm −3 and corresponding values of Tgas and AV are chosen according to (Katz et al (1999) for olivine) (Katz et al (1999) for amorphous) (Lipshtat, Biham & Herbst 2004) 2d show the progressive increment of deuterium fractionation in comparison to the non-deuterated case (Fig. 2a).…”

Section: Composition Of Grain Mantles With Deuterated Speciesmentioning

confidence: 99%

Deuterium enrichment of the interstellar grain mantle

Das¹,

Sahu²,

Majumdar³

et al. 2015

Mon. Not. R. Astron. Soc.

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We carry out Monte-Carlo simulation to study deuterium enrichments of interstellar grain mantles under various physical conditions. Based on the physical properties, various types of clouds are considered. We find that in diffuse cloud regions, very strong radiation fields persists and hardly a few layers of surface species are formed. In translucent cloud regions with a moderate radiation field, significant number of layers would be produced and surface coverage is mainly dominated by photo-dissociation products such as, C, CH 3 , CH 2 D, OH and OD. In the intermediate dense cloud regions (having number density of total hydrogen nuclei in all forms ∼ 2 × 10 4 cm −3 ), water and methanol along with their deuterated derivatives are efficiently formed. For much higher density regions (∼ 10 6 cm −3 ), water and methanol productions are suppressed but surface coverages of CO, CO 2 , O 2 , O 3 are dramatically increased. We find a very high degree of fractionation of water and methanol. Observational results support a high fractionation of methanol but surprisingly water fractionation is found to be low. This is in contradiction with our model results indicating alternative routes for de-fractionation of water. Effects of various types of energy barriers are also studied. Moreover, we allow grain mantles to interact with various charged particles (such as H + , Fe + , S + and C + ) to study the stopping power and projected range of these charged particles on various target ices.

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“…In the simulations presented below, the density of adsorption sites was s = 5 × 10 13 (sites cm −2 ), the activation energies were E 0 = 22 meV for diffusion and E 1 = 32 meV for desorption. These parameters are rounded values of the experimental results for hydrogen recombination on silicates [52].…”

Section: A Rate Equationsmentioning

confidence: 99%

Efficient stochastic simulations of complex reaction networks on surfaces

Barzel

Biham

2007

The Journal of Chemical Physics

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Surfaces serve as highly efficient catalysts for a vast variety of chemical reactions. Typically, such surface reactions involve billions of molecules which diffuse and react over macroscopic areas.Therefore, stochastic fluctuations are negligible and the reaction rates can be evaluated using rate equations, which are based on the mean-field approximation. However, in case that the surface is partitioned into a large number of disconnected microscopic domains, the number of reactants in each domain becomes small and it strongly fluctuates. This is, in fact, the situation in the interstellar medium, where some crucial reactions take place on the surfaces of microscopic dust grains. In this case rate equations fail and the simulation of surface reactions requires stochastic methods such as the master equation. However, in the case of complex reaction networks, the master equation becomes infeasible because the number of equations proliferates exponentially.To solve this problem, we introduce a stochastic method based on moment equations. In this method the number of equations is dramatically reduced to just one equation for each reactive species and one equation for each reaction. Moreover, the equations can be easily constructed using a diagrammatic approach. We demonstrate the method for a set of astrophysically relevant networks of increasing complexity. It is expected to be applicable in many other contexts in which problems that exhibit analogous structure appear, such as surface catalysis in nanoscale systems, aerosol chemistry in stratospheric clouds and genetic networks in cells.

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Molecular Hydrogen Formation on Astrophysically Relevant Surfaces

Cited by 324 publications

References 21 publications

Interstellar H adsorption and H₂formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

Interstellar H adsorption and H₂formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

Deuterium enrichment of the interstellar grain mantle

Efficient stochastic simulations of complex reaction networks on surfaces

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Molecular Hydrogen Formation on Astrophysically Relevant Surfaces

Cited by 324 publications

References 21 publications

Interstellar H adsorption and H2formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

Interstellar H adsorption and H2formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

Deuterium enrichment of the interstellar grain mantle

Efficient stochastic simulations of complex reaction networks on surfaces

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Product

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Interstellar H adsorption and H₂formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

Interstellar H adsorption and H₂formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study