Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores

Kalvāns, Juris; Shmeld, I.

doi:10.1051/0004-6361/201014190

Cited by 30 publications

(49 citation statements)

References 33 publications

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“…N hop = 200 is the assumed number of steps required for molecules to eventually emerge to surface from a cavity or to find a cavity opening and delve into it (for surface species). This process is a deviation from the previous models by Kalvāns & Shmeld (2010), because it takes into account the connection of cavities to the surface, while still regarding them as separate phases. Cavity openings can be regarded as good adsorption sites and they can be easily blocked at 10 K by common species, such as H 2 O, NH 3 or CO 2 .…”

Section: Surface-cavity Diffusionmentioning

confidence: 94%

“…While modeling of surface reactions dates back to 1970s (e.g., Watson & Salpeter 1972), the investigation of active subsurface ice chemistry is relatively recent. Cuppen & Herbst (2007) and Kalvāns & Shmeld (2010) have published the first such models with the Monte Carlo technique and the rate equations method, respectively. Detailed ice mantle modeling provides important information about several astrochemistry problems, e.g., ice growth and structure, hydrogenation and oxidation of CO on grains, and production of complex organic molecules (Cuppen et al 2009;Kalvāns & Shmeld 2013;Garrod 2013a,b).…”

Section: Introductionmentioning

confidence: 99%

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Cosmic-Ray Induced Diffusion in Interstellar Ices

Kalvāns

2014

Open Astronomy

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Abstract.Cosmic rays are able to heat interstellar dust grains. This may enhance molecule mobility in icy mantles that have accumulated on the grains in dark cloud cores. A three-phase astrochemical model was used to investigate the molecule mobility in interstellar ices. Specifically, diffusion through pores in ice between the subsurface mantle and outer surface, assisted by whole-grain heating, was considered. It was found that the pores can serve as an efficient transport route for light species. The diffusion of chemical radicals from the mantle to the outer surface are most effective. These species accumulate in the mantle because of photodissociation by the cosmic-ray induced photons. The faster diffusion of hydrogen within the warm ice enhances the hydrogenation of radicals on pore surfaces. The overall result of the whole grain heating-induced radial diffusion in ice are higher abundances of ice species, whose synthesis involve light radicals. Examples of stable species synthesized this way include complex organic molecules, OCS, H 2 O 2 and cyanoplyynes.

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Section: Surface-cavity Diffusionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Cosmic-Ray Induced Diffusion in Interstellar Ices

Kalvāns

2014

Open Astronomy

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“…The estimated abundance is onlydetermined based on the SO molecules released into the gas phase; thereforethe total SO abundance, including that on the grain surfaces, may be significantly higher. Kalvāns & Shmeld (2010) have calculated the abundances of various species in interstellar molecular clouds based on their simple kinetic model, in which the gas phase, grain surface, and H-poor subsurface pore reactions are included. These researchers demonstrated that y 10 …”

Section: So So Warmmentioning

confidence: 99%

Comprehensive Study of Thermal Desorption of Grain-surface Species by Accretion Shocks around Protostars

Miura

Yamamoto

Nomura

et al. 2017

ApJ

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We conducted numerical simulations of the dust heating in accretion shocks induced by the interaction between the infalling envelope and the Keplerian disk surrounding a protostar, in order to investigate the thermal desorption of molecules from the dust-grain surfaces. It is thought that the surfaces of the amorphous dust grains are inhomogeneous; various adsorption sites with different binding energies should therefore exist. We assumed that the desorption energy has a Gaussian distribution and investigated the effect of the desorption energy distribution on the desorption-efficiency evaluation. We calculated the desorption fractions of the grain-surface species for wide ranges of input parameters and summarized our results in a shock diagram. The resultingshock diagram suggests that the enhanced line emissions around protostars observed using the Atacama Large Millimeter Array cannot be explained by the thermal desorption in an accretion shockif typical interstellar dust-grain sizes ( 0.1 m m ) and a single desorption energy are considered. On the other hand, if significantly smaller dust grains are the main grain-surface species carriers and the desorption energy has a Gaussian distribution, the origin of the enhanced line emission can be explained by the accretion shock heating scenario for all of the three protostars examined in this study: IRAS 04368+2557, IRAS 04365+2535, and IRAS 16293-2422. The small-grain-carrier supposition is quite reasonable when the dust grains have a power-law size distribution because the smaller grains primarily contribute to the dust-grain surface area.

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“…A number of approximate or precise micro-and macroscopic Monte Carlo techniques have been proposed to overcome this issue (e.g., Biham et al 2001;Charnley 2001;Lipshtat and Biham 2004;Stantcheva and Herbst 2004;Chang et al 2005;Garrod 2008;. Another challenge is to account for the multilayered nature of dust-grain ice mantles, and to take all relevant processes into account in the modeling, e.g., inter-lattice diffusion, mobility/immobility of reactants, desorption, porosity trapping (see Chang et al 2007;Kalvāns and Shmeld 2010;Wolff et al 2011;. A further obstacle in both approaches (rate equation and stochastic) is the lack of appropriate laboratory data on binding energies and desorption efficiencies of molecular ices of astrophysical interest, as well as the energy barriers and branching ratios for surface reactions.…”

Section: Introductionmentioning

confidence: 99%

Grain Surface Models and Data for Astrochemistry

et al. 2017

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The cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions.

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Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores

Cited by 30 publications

References 33 publications

Cosmic-Ray Induced Diffusion in Interstellar Ices

Cosmic-Ray Induced Diffusion in Interstellar Ices

Comprehensive Study of Thermal Desorption of Grain-surface Species by Accretion Shocks around Protostars

Grain Surface Models and Data for Astrochemistry

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