Chemistry on Rotating Grain Surfaces: Ro-thermal Desorption of Molecules from Ice Mantles

Hoang, Thiem; Tung, Ngo Duy

doi:10.3847/1538-4357/ab4810

Cited by 15 publications

(23 citation statements)

References 72 publications

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“…We note that even in the hot inner region where thermal sublimation is active, rotational desorption and rothermal desorption (Hoang & Tung 2019) are more efficient than the classical sublimation for molecules with high binding energy such as water and COMs.…”

Section: Application: Rotational Desorption Of Ice Mantles In Hot Cormentioning

confidence: 87%

Rotational Desorption of Ice Mantles from Suprathermally Rotating Grains around Young Stellar Objects

Hoang

Tram

2020

ApJ

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Ice mantles on dust grains play a central role in astrochemistry. Water and complex organic molecules (COMs) are thought to first form on the ice mantles and subsequently are released into the gas phase due to star formation activity. However, the critical question is whether ice mantles can survive stellar radiation when grains are being heated from T d ∼ 10 K to 100 K. In this paper, we first study the effect of suprathermal grain rotation driven by the intense radiation of young stellar objects (YSOs) on the ice mantles. We find that the entire ice mantles can be disrupted into small fragments by centrifugal stress before the water ice and COMs desorb via thermal sublimation. We then study the consequence of resulting ice fragments and find that tiny fragments of radius a 10Å exhibit transient release of COMs due to thermal spikes, whereas larger fragments can facilitate thermal sublimation at much higher rates than from the original icy grain or the same rate but with temperatures of ∼ 20 − 40 K lower. We find that rotational desorption is efficient for hot cores/corinos from the inner to outer regions where the temperature drops to T gas ∼ 40 K and n H ∼ 10 4 cm −3 . We discuss the implications of this mechanism for desorption of COMs and water ice in various environments, including outflow cavity walls, photodissociation regions, and protoplanetary disks. Finally, we show that very large aggregate grains can be disrupted into individual icy grains via rotational disruption mechanism, followed by rotational desorption of ice mantles.

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Section: Application: Rotational Desorption Of Ice Mantles In Hot Cormentioning

confidence: 87%

Rotational Desorption of Ice Mantles from Suprathermally Rotating Grains around Young Stellar Objects

Hoang

Tram

2020

ApJ

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“…We note that even in the hot inner region where thermal sublimation is active, rotational desorption and ro-thermal desorption (Hoang and Tung [45]) are more efficient than the classical sublimation for molecules with high binding energy such as water and COMs. Gas temperature and grain disruption size vs. radius for an envelope around a high-mass protostar.…”

Section: Rotational Desorption Of Ice In Star-forming Regions Around Ysosmentioning

confidence: 91%

“…Figure 26 (left panel) shows that large grains can be disrupted into nanoparticles in a vast area of the surface and intermediate layers by the RATD mechanism. Moreover, PAHs/nanoparticles frozen in the icy grain mantles can desorb from the ice mantle via the ro-thermal desorption mechanism (Hoang and Tung [45]; right panel). Thus, if grains are small enough (a 1 µm) to be mixed with the gas by turbulence, they can escape grain settling and coagulation in the disk mid-plane and are transported to the surface layer (Dullemond and Dominik [136], Fromang and Nelson [137]).…”

Section: Rotational Disruption Of Dust and Ice In Protoplanetary Disksmentioning

confidence: 99%

“…Suprathermal rotation by RATs is found to be important for surface chemistry in star-forming and photodissociation regions. It is found that suprathermal rotation can assist thermal desorption of molecules from the ice mantle, which enables molecule desorption at temperatures T d < 100 K, lower than classical thermal sublimation threshold (Section 2, Hoang and Tram [44], Hoang and Tung [45]). The rate of surface chemical reactions depends on the mobility of adsorbed species on the grain surface (Watson and Salpeter [80], Hasegawa et al [171]).…”

Section: Astrochemistry On Rotating Grain Surfacesmentioning

confidence: 99%

“…The reason is that water and complex molecules in the ice mantles sublimate at temperatures of T d > 100 K (Herbst and van Dishoeck [2]), which corresponds to U > 10 5 , that is, much stronger radiation fields than the ISRF for which RATD is important. As shown in Hoang and Tram [44] and Hoang and Tung [45], the grain suprathermal rotation also affects the chemical composition and metallicity of the gas because ice mantles on the grain surface are easily disrupted by centrifugal stress.…”

Section: Introductionmentioning

confidence: 99%

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Rotational Disruption of Astrophysical Dust and Ice—Theory and Applications

Hoang

2020

Galaxies

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Dust is an essential component of the interstellar medium (ISM) and plays an important role in many different astrophysical processes and phenomena. Traditionally, dust grains are known to be destroyed by thermal sublimation, Coulomb explosions, sputtering, and shattering. The first two mechanisms arise from the interaction of dust with intense radiation fields and high-energy photons (extreme UV), which work in a limited astrophysical environment. The present review is focused on a new destruction mechanism present in the dust-radiation interaction that is effective in a wide range of radiation fields and has ubiquitous applications in astrophysics. We first describe this new mechanism of grain destruction, namely rotational disruption induced by Radiative Torques (RATs) or RAdiative Torque Disruption (RATD). We then discuss rotational disruption of nanoparticles by mechanical torques due to supersonic motion of grains relative to the ambient gas, which is termed MEchanical Torque Disruption (METD). These two new mechanisms modify properties of dust and ice (e.g., size distribution and mass), which affects observational properties, including dust extinction, thermal and nonthermal emission, and polarization. We present various applications of the RATD and METD mechanisms for different environments, including the ISM, star-forming regions, astrophysical transients, and surface astrochemistry.

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Efficiency of non-thermal desorptions in cold-core conditions

Wakelam

Dartois

Chabot

et al. 2021

A&A

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Context. Under cold conditions in dense cores, gas-phase molecules and atoms are depleted from the gas-phase to the surface of interstellar grains. Considering the time scales and physical conditions within these cores, a portion of these molecules has to be brought back into the gas-phase to explain their observation by milimeter telescopes. Aims. We tested the respective efficiencies of the different mechanisms commonly included in the models (photo-desorption, chemical desorption, and cosmic-ray-induced whole-grain heating). We also tested the addition of sputtering of ice grain mantles via a collision with cosmic rays in the electronic stopping power regime, leading to a localized thermal spike desorption that was measured in the laboratory. Methods. The ice sputtering induced by cosmic rays has been added to the Nautilus gas-grain model while the other processes were already present. Each of these processes were tested on a 1D physical structure determined by observations in TMC1 cold cores. We focused the discussion on the main ice components, simple molecules usually observed in cold cores (CO, CN, CS, SO, HCN, HC3N, and HCO+), and complex organic molecules (COMs such as CH3OH, CH3CHO, CH3OCH3, and HCOOCH3). The resulting 1D chemical structure was also compared to methanol gas-phase abundances observed in these cores. Results. We found that all species are not sensitive in the same way to the non-thermal desorption mechanisms, and the sensitivity also depends on the physical conditions. Thus, it is mandatory to include all of them. Chemical desorption seems to be essential in reproducing the observations for H densities smaller than 4 × 104 cm−3, whereas sputtering is essential above this density. The models are, however, systematically below the observed methanol abundances. A more efficient chemical desorption and a more efficient sputtering could better reproduce the observations. Conclusions. In conclusion, the sputtering of ices by cosmic-rays collisions may be the most efficient desorption mechanism at high density (a few 104 cm−3 under the conditions studied here) in cold cores, whereas chemical desorption is still required at smaller densities. Additional works are needed on both mechanisms to assess their efficiency with respect to the main ice composition.

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Chemistry on Rotating Grain Surfaces: Ro-thermal Desorption of Molecules from Ice Mantles

Cited by 15 publications

References 72 publications

Rotational Desorption of Ice Mantles from Suprathermally Rotating Grains around Young Stellar Objects

Rotational Desorption of Ice Mantles from Suprathermally Rotating Grains around Young Stellar Objects

Rotational Disruption of Astrophysical Dust and Ice—Theory and Applications

Efficiency of non-thermal desorptions in cold-core conditions

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