OH Formation from O and H Atoms Physisorbed on a Graphitic Surface through the Langmuir−Hinshelwood Mechanism: A Quasi-Classical Approach

Bergeron, Hervé; Rougeau, N.; Sidis, V.; Sizun, M.; Teillet‐Billy, D.; Aguillon, F.

doi:10.1021/jp8050966

Cited by 43 publications

(55 citation statements)

References 40 publications

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“…Although it is an empirical approach, it allows sorting among the products that should undergo the chemical desorption. The basic idea underlying our proposition is inspired by dynamic calculations in specific systems such as H+H on graphite (Morisset et al 2004;Bachellerie et al 2007) or O+H on graphite (Bergeron et al 2008). We have illustrated the mechanism of this scenario in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Garrod et al (2007) have previously proposed a formula in their models that can be used to describe the chemical desorption (or reactive desorption). They derived the probability of A24, page 4 of 6 Bergeron et al (2008); (c) Al-Halabi & van Dishoeck (2007), Amiaud et al (2007); (d) Pirronello et al (1997); (e) Amiaud et al (2006) for low coverage; ( f ) Minissale et al (2015); (g) Dulieu et al (2013); (h) Speedy et al (1996), Fraser et al (2001 energy derived of 5800 K with pre-factor of 10 15 s −1 here corrected to have a pre-factor of 10 12 s −1 ; (i) Noble et al (2012a); ( (2)) that include division between the degree of freedom and the fraction of kinetic energy after bounce ( is mass dependent). In red we show the equal share of energy and the constant value of .…”

Section: Theoretical Estimate Of the Desorption Efficiencymentioning

confidence: 99%

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Dust as interstellar catalyst

Minissale

Dulieu

Cazaux

et al. 2015

A&A

182

227

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Context. The presence of dust in the interstellar medium has profound consequences on the chemical composition of regions where stars are forming. Recent observations show that many species formed onto dust are populating the gas phase, especially in cold environments where UV-and cosmic-ray-induced photons do not account for such processes. Aims. The aim of this paper is to understand and quantify the process that releases solid species into the gas phase, the so-called chemical desorption process, so that an explicit formula can be derived that can be included in astrochemical models. Methods. We present a collection of experimental results of more than ten reactive systems. For each reaction, different substrates such as oxidized graphite and compact amorphous water ice were used. We derived a formula for reproducing the efficiencies of the chemical desorption process that considers the equipartition of the energy of newly formed products, followed by classical bounce on the surface. In part II of this study we extend these results to astrophysical conditions. Results. The equipartition of energy correctly describes the chemical desorption process on bare surfaces. On icy surfaces, the chemical desorption process is much less efficient, and a better description of the interaction with the surface is still needed. Conclusions. We show that the mechanism that directly transforms solid species into gas phase species is efficient for many reactions.

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Section: Discussionmentioning

confidence: 99%

Section: Theoretical Estimate Of the Desorption Efficiencymentioning

confidence: 99%

Dust as interstellar catalyst

Minissale

Dulieu

Cazaux

et al. 2015

A&A

182

227

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“…Owing to the lack of laboratory measurements for the binding energy of atomic oxygen on water ice or other surfaces, a binding energy of T b,O = 800 K (Tielens & Hagen 1982) was assumed. This results in a freeze-out temperature of T dust ∼ 15 K. Recent theoretical work and laboratory data point to binding energies that could be more of the order of T b,O = 1500 K on amorphous silicate or graphite surfaces (Bergeron et al 2008;He et al 2014), for which the freeze-out threshold temperature would be raised to around T dust ∼ 35 K. If such a high value would also apply to the binding of O on water ice, about 2−5 times more material (15−35% of the column density within the water freeze-out zone) would be found in a region where atomic oxygen can still be converted into water ice, effectively increasing the overall water abundance and thus requiring an even shorter pre-stellar phase.…”

Section: Water Icementioning

confidence: 99%

Water in low-mass star-forming regions withHerschel

Schmalzl

Visser

Walsh

et al. 2014

A&A

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Aims. Our aim is to determine the critical parameters in water chemistry and the contribution of water to the oxygen budget by observing and modelling water gas and ice for a sample of eleven low-mass protostars, for which both forms of water have been observed. Methods. A simplified chemistry network, which is benchmarked against more sophisticated chemical networks, is developed that includes the necessary ingredients to determine the water vapour and ice abundance profiles in the cold, outer envelope in which the temperature increases towards the protostar. Comparing the results from this chemical network to observations of water emission lines and previously published water ice column densities, allows us to probe the influence of various agents (e.g., far-ultraviolet (FUV) field, initial abundances, timescales, and kinematics). Results. The observed water ice abundances with respect to hydrogen nuclei in our sample are 30−80 ppm, and therefore contain only 10-30% of the volatile oxygen budget of 320 ppm. The keys to reproduce this result are a low initial water ice abundance after the pre-collapse phase together with the fact that atomic oxygen cannot freeze-out and form water ice in regions with T dust > ∼ 15 K. This requires short prestellar core lifetimes < ∼ 0.1 Myr. The water vapour profile is shaped through the interplay of FUV photodesorption, photodissociation, and freeze-out. The water vapour line profiles are an invaluable tracer for the FUV photon flux and envelope kinematics. Conclusions. The finding that only a fraction of the oxygen budget is locked in water ice can be explained either by a short precollapse time of < ∼ 0.1 Myr at densities of n H ∼ 10 4 cm −3 , or by some other process that resets the initial water ice abundance for the post-collapse phase. A key for the understanding of the water ice abundance is the binding energy of atomic oxygen on ice.

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“…In particular, we concentrate on grain surface chemistry, and the amounts of species that this process releases into the gas phase. The interactions between species and carbon surfaces (graphite or amorphous carbon) has received much attention (Ghio et al 1980;Pirronello et al 1997;Jeloaica & Sidis 1999;Sha & Jackson 2002;Bergeron et al 2008). Theoretical and experimental studies of the interactions between chemical species and these types of surfaces provide a considerable number of constraints for our model.…”

Section: Introductionmentioning

confidence: 99%

Water formation on bare grains: When the chemistry on dust impacts interstellar gas

Cazaux¹,

Cobut

Marseille

et al. 2010

A&A

100

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Context. Water and O 2 are important gas phase ingredients for cooling dense gas when forming stars. On dust grains, H 2 O is an important constituent of the icy mantle in which a complex chemistry is taking place, as revealed by hot core observations. The formation of water can occur on dust grain surfaces, and can impact gas phase composition. Aims. The formation of molecules such as OH, H 2 O, HO 2 and H 2 O 2 , as well as their deuterated forms and O 2 and O 3 is studied to assess how the chemistry varies in different astrophysical environments, and how the gas phase is affected by grain surface chemistry. Methods. We use Monte Carlo simulations to follow the formation of molecules on bare grains as well as the fraction of molecules released into the gas phase. We consider a surface reaction network, based on gas phase reactions, as well as UV photo-dissociation of the chemical species.Results. We show that grain surface chemistry has a strong impact on gas phase chemistry, and that this chemistry is very different for different dust grain temperatures. Low temperatures favor hydrogenation, while higher temperatures favor oxygenation. Also, UV photons dissociate the molecules on the surface, which can subsequently reform. The formation-destruction cycle increases the amount of species released into the gas phase. We also determine the timescales to form ices in diffuse and dense clouds, and show that ices are formed only in shielded environments, as supported by observations.

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OH Formation from O and H Atoms Physisorbed on a Graphitic Surface through the Langmuir−Hinshelwood Mechanism: A Quasi-Classical Approach

Cited by 43 publications

References 40 publications

Dust as interstellar catalyst

Dust as interstellar catalyst

Water in low-mass star-forming regions withHerschel

Water formation on bare grains: When the chemistry on dust impacts interstellar gas

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