Dust as interstellar catalyst

Cazaux, S.; Minissale, Marco; Dulieu, F.; Hocuk, S.

doi:10.1051/0004-6361/201527187

Cited by 40 publications

(43 citation statements)

References 51 publications

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“…Our model is described in Cazaux et al (2016). CO molecules originating from the gas phase arrive at a random time and location to the substrate, and follow a random path within the ice.…”

Section: Simulationsmentioning

confidence: 99%

“…We used a three-phase chemical model that combines gas-phase chemistry with surface and bulk chemistry. The grain surface chemistry model (surface + bulk) takes into account the different binding energies of the species on bare or icy surfaces and includes evaporation, reactions, photodissociation, and thermal and photodesorption processes, which transform surface species either into other surface species or into gas-phase species, as in Cazaux et al (2016). Note that, in this study, we only consider CO freeze out on the dust surface but do not allow surface reactions with CO. Inaddition, our model does not take into account the diffusion of species from bulk to surface and from surface to bulk.…”

Section: Astrophysical Applicationsmentioning

confidence: 99%

“…In this sense, when the coverage has reached one layer, the accreting species become bulk species with higher energies and lower diffusion rates (because the diffusion depends on the binding energy). The gas-phase chemical model is adopted from the KIDA database (Wakelam et al 2012), while the surface chemistry model is described in Cazaux et al (2016). The input parameters to mimic the temperature and density profile of a pre-stellar core are taken from Keto & Caselli (2010) and shown in Figure 16.…”

Section: Astrophysical Applicationsmentioning

confidence: 99%

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CO Depletion: A Microscopic Perspective

Cazaux

Martín-Doménech

Chen

et al. 2017

ApJ

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In regions where stars form, variations in density and temperature can cause gas to freeze out onto dust grains forming ice mantles, which influences the chemical composition of a cloud. The aim of this paper is to understand in detail the depletion (and desorption) of CO on (from) interstellar dust grains. Experimental simulations were performed under two different (astrophysically relevant) conditions. In parallel, Kinetic Monte Carlo simulations were used to mimic the experimental conditions. In our experiments, CO molecules accrete onto water ice at temperatures below 27 K, with a deposition rate that does not depend on the substrate temperature. During the warm-up phase, the desorption processes do exhibit subtle differences, indicating the presence of weakly bound CO molecules, therefore highlighting a low diffusion efficiency. IR measurements following the ice thickness during the TPD confirm that diffusion occurs at temperatures close to the desorption. Applied to astrophysical conditions, in a pre-stellar core, the binding energies of CO molecules, ranging between 300 and 850 K, depend on the conditions at which CO has been deposited. Because of this wide range of binding energies, the depletion of CO as a function of A V is much less important than initially thought. The weakly bound molecules, easily released into the gas phase through evaporation, change the balance between accretion and desorption, which result in a larger abundance of CO at high extinctions. In addition, weakly bound CO molecules are also more mobile, and this could increase the reactivity within interstellar ices.

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“…Our model is described in Cazaux et al (2016). CO molecules originating from the gas phase arrive at a random time and location to the substrate, and follow a random path within the ice.…”

Section: Simulationsmentioning

confidence: 99%

Section: Astrophysical Applicationsmentioning

confidence: 99%

Section: Astrophysical Applicationsmentioning

confidence: 99%

See 1 more Smart Citation

CO Depletion: A Microscopic Perspective

Cazaux

Martín-Doménech

Chen

et al. 2017

ApJ

Self Cite

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“…In addition, the rate constant increase is noteworthy only below ∼ 200 K, which also limits spatially the impact of the enhanced water formation. In addition, surface chemistry, especially chemical desorption from surfaces, can enhance the gas-phase water abundance around the snowline (Cazaux et al 2016); however, this process needs to be studied in a future work. The Herbig disk model is flatter than the T Tauri disk model and has a more extended region where the temperature ranges between 200 K and the freeze-out of water.…”

Section: Use Of Correct Reaction Rate Constantsmentioning

confidence: 99%

The role of atom tunneling in gas-phase reactions in planet-forming disks

Meisner

Kamp

Thi

et al. 2019

A&A

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Context. Gas-phase chemical reactions of simple molecules have been recently revised to include atom tunneling at very low temperatures. This paper investigates the impact of the increased reaction rate constant due to tunneling effects on planet-forming disks. Aims. Our aim is to quantify the astrophysical implications of atom tunneling for simple molecules that are frequently used to infer disk structure information or to define the initial conditions for planet (atmosphere) formation. Methods. We quantify the tunneling effect on reaction rate constants by using H 2 + OH → H 2 O + H as a scholarly example in comparison to previous UMIST2012 rate constants. In a chemical network with 1299 reactions, we identify all chemical reactions that could show tunneling effects. We devise a simple formulation of reaction rate constants that overestimates tunneling and screen a standard T Tauri disk model for changes in species abundances. For those reactions found to be relevant, we find values of the most recent literature for the rate constants including tunneling and compare the resulting disk chemistry to the standard disk model(s), a T Tauri and a Herbig disk. Results. The rate constants in the UMIST2012 database in many cases already capture tunneling effects implicitly, as seen in the curvature of the Arrhenius plots of some reactions at low temperature. A rigorous screening procedure identified three neutral-neutral reactions where atom tunneling could change simple molecule abundances. However, by adopting recent values of the rate constants of these reactions and due to the layered structure of planet-forming disks, the effects are limited to a small region between the ion-molecule dominated regime and the ice reservoirs where cold (< 250 K) neutral-neutral chemistry dominates. Abundances of water close to the midplane snowline can increase by a factor of two at most compared to previous results with UMIST2012 rates. Observables from the disk surface, such as high excitation (> 500 K) water line fluxes, decrease by 60% at most when tunneling effects are explicitly excluded. On the other hand, disk midplane quantities relevant for planet formation such as the C-to-O ratio and also the ice-to-rock ratio are clearly affected by these gas-phase tunneling effects.

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“…In the model by Du et al (2012) a desorption mechanism is included that is based on the release of excess energy during the molecule formation. This concept has also been applied by Cazaux et al (2016) and Minissale et al (2016). Initially, and already including gas-and solid-phase reactions, Du et al (2012) constrained themselves to stationary and constant physical conditions in their model.…”

Section: Introductionmentioning

confidence: 99%

Deep search for hydrogen peroxide toward pre- and protostellar objects

Fuchs

Witsch

Herberth

et al. 2020

A&A

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Context. In the laboratory, hydrogen peroxide (HOOH) was proven to be an intermediate product in the solid-state reaction scheme that leads to the formation of water on icy dust grains. When HOOH desorbs from the icy grains, it can be detected in the gas phase. In combination with water detections, it may provide additional information on the water reaction network. Hydrogen peroxide has previously been found toward ρ Oph A. However, further searches for this molecule in other sources failed. Hydrogen peroxide plays a fundamental role in the understanding of solid-state water formation and the overall water reservoir in young stellar objects (YSOs). Without further HOOH detections, it is difficult to assess and develop suitable chemical models that properly take into account the formation of water on icy surfaces. Aims. The objective of this work is to identify HOOH in YSOs and thereby constrain the grain surface water formation hypothesis. Methods. Using an astrochemical model based on previous work in combination with a physical model of YSOs, the sources R CrA-IRS 5A, NGCC1333-IRAS 2A, L1551-IRS 5, and L1544 were identified as suitable candidates for an HOOH detection. Long integration times on the APEX 12m and IRAM 30m telescopes were applied to search for HOOH signatures in these sources. Results. None of the four sources under investigation showed convincing spectral signatures of HOOH. The upper limit for HOOH abundance based on the noise level at the frequency positions of this molecule for the source R CrA-IRS 5A was close to the predicted value. For NGC1333-IRAS 2A, L1544, and L1551-IRS 5, the model overestimated the hydrogen peroxide abundances. Conclusions. HOOH remains an elusive molecule. With only one secure cosmic HOOH source detected so far, namely ρ Oph A, the chemical model parameters for this molecule cannot be sufficiently well determined or confirmed in existing models. Possible reasons for the nondetections of HOOH are discussed.

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Dust as interstellar catalyst

Cited by 40 publications

References 51 publications

CO Depletion: A Microscopic Perspective

CO Depletion: A Microscopic Perspective

The role of atom tunneling in gas-phase reactions in planet-forming disks

Deep search for hydrogen peroxide toward pre- and protostellar objects

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