Surface astrochemistry: a computational chemistry perspective

Cuppen, H. M.; Fredon, A.; Lamberts, Thanja; Penteado, Eduardo Monfardini; Simons, Michiel; Walsh, Catherine

doi:10.1017/s1743921317009929

Cited by 3 publications

(5 citation statements)

References 32 publications

(40 reference statements)

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“…Microscopic Monte Carlo simulation, which records the position of each adsorbed species in ice mantle, is suitable for such cold ice chemistry (e.g. Cuppen et al 2018) (see also Garrod & Clements on page 429). Microscopic Monte Carlo simulation is, however, computationally expensive; most of the CPU time is consumed to follow the thermal hopping of very volatile species such as H atom, once the temperature starts to rise.…”

Section: Com Formation Mechanismsmentioning

confidence: 99%

Gas-dust chemistry of volatiles in the star and planetary system formation

Aikawa

Furuya

2019

Proc. IAU

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The focus of this work is on two topics: (i) formation of complex organic molecules (COMs) and (ii) isotope fractionation. Various COMs, which are C, H-containing molecules consisting of 6 atoms and more, have been detected in the central warm region of protostellar cores. Most of this review is about gas-grain chemical models, which have been constructed to evaluate the mechanisms and efficiency of the COM formation. The relevant physical and chemical processes are investigated in laboratory experiments, as reported in other articles in this volume.The isotope fractionation of volatile elements is observed in both the interstellar medium (ISM) and Solar system material. While exothermic exchange reactions enrich molecules with heavier isotopes such as Deuterium, the isotope selective photodissociation can be coupled with ice formation to enrich the ice mantle with rare isotopes. The efficiency of this fractionation depends on the photodesorption yields, which has been studied in laboratory experiments.

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“…The interested reader can found more about modeling interstellar ice in the recent papers by Zamirri et al 14 and Cuppen et al 32 …”

Section: Introductionmentioning

confidence: 99%

“…The interested reader can found more about modeling interstellar ice in the recent papers by Zamirri et al 14 and Cuppen et al 32 In this paper, we will describe a new approach to automatically building up an amorphous icy grain model constituted by several hundreds of water molecules. We labeled our models as "realistic", not based on a size criterion only but requiring the following essential features: (i) the grain should not be minimal, i.e., envisaging 20−30 water molecules only, as usually found in the literature, but includes at least few hundreds water molecules; (ii) the hydrogen bond features within the icy grain should be accurately represented by adopting a proper quantum level of theory; (iii) the ice should be amorphous by construction, avoiding the usual approach of heating at high T and sudden cooling of a crystalline ice model, which has no counterpart in the grain evolution in the ISM.…”

Section: ■ Introductionmentioning

confidence: 99%

Computer Generated Realistic Interstellar Icy Grain Models: Physicochemical Properties and Interaction with NH₃

Germain

Tinacci

Pantaleone

et al. 2022

ACS Earth Space Chem.

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Interstellar grains are composed by a rocky core (usually amorphous silicates) covered by an icy mantle, the most abundant molecule being H 2 O followed by CO, CO 2 , NH 3 , and also radicals in minor quantities. In dense molecular clouds, gas-phase chemical species freeze onto the grain surface, making it an important reservoir of molecular diversity/complexity whose evolution leads to interstellar complex organic molecules (iCOMs). Many different models of water clusters have appeared in the literature, but without a systematic study on the properties of the grain (such as the H-bonds features, the oxygen radial distribution function, the dangling species present on the mantle surface, the surface electrostatic potential, etc.). In this work, we present a computer procedure (ACO-FROST) grounded on the newly developed semiempirical GFN2 tight-binding quantum mechanical method and the GFN-FF force field method to build-up structures of amorphous ice of large size. These methods show a very favorable accuracy/cost ratio as they are ideally designed to take noncovalent interactions into account. ACO-FROST program can be tuned to build grains of different composition mimicking dirty icy grains. These icy grain models allow studying the adsorption features (structure, binding energy, vibrational frequencies, etc.) of relevant species on a large variety of adsorption sites so to obtain a statistically meaningful distribution of the physicochemical properties of interest to be transferred in numerical models. As a test case, we computed the binding energy of ammonia adsorbed at the different sites of the icy grain surface, showing a broad distribution not easily accounted for by other more size limited icy grain models. Our method is also the base for further refinements, adopting the present grain in a more rigorous QM:MM treatment, capable of giving binding energies within the chemical accuracy.

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“…Ice-covered grains found in interstellar and prestellar nebulae offer active sites for chemistry to occur − that are often both different and more favorable than the limited gas phase chemistry that can occur at the very cold temperatures (∼15 K) and low densities (as low as 10 3 m –3 ) that exist in these sources . A wide variety of heterogeneous pathways to form small compounds have been characterized via both theory and experiment that involve neutral and charged systems. − There is great interest in the formation of complex organic molecules (COMs) or their precursors, particularly in protostellar sources, since they may provide insight into how the compounds necessary for biopoiesis made their way to the primordial Earth. Ice chemistry is thought to contribute significantly to COM formation. ,,− …”

Section: Introductionmentioning

confidence: 99%

“…A wide variety of heterogeneous pathways to form small compounds have been characterized via both theory and experiment that involve neutral and charged systems. − There is great interest in the formation of complex organic molecules (COMs) or their precursors, particularly in protostellar sources, since they may provide insight into how the compounds necessary for biopoiesis made their way to the primordial Earth. Ice chemistry is thought to contribute significantly to COM formation. ,,− …”

Section: Introductionmentioning

confidence: 99%

Icy Grain Mantle Surface Astrochemistry of MgNC: The Emergence of Metal Ion Catalysis Studied via Model Ice Cluster Calculations

Woon

2022

J. Phys. Chem. A

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One of a small number of known magnesium-containing astromolecules, magnesium isocyanide (MgNC) was first detected in 1986. MgNC is an intriguing reactant to consider: it is an open-shell radical in which its metal atom forms a bond with CN that is a mixture of ionic and covalent character. While its gas phase astrochemistry has received prior attention, the grain surface chemistry of MgNC has never been studied. Because of its ionic character, MgNC is found to interact far more strongly with an ice surface than molecules with a greater degree of covalency. As a radical, it may react with closed-shell molecules deposited from the gas phase. In this work, cluster calculations treated with density functional theory and correlation consistent basis sets were used to model the deposition of MgNC on clusters containing 17 and 24 water molecules, which were then allowed to react with acetylene (HCCH) and hydrogen cyanide (HCN) as well as with H atoms. The addition of H to MgNC–nH2O yields hydromagnesium isocyanide (HMgNC), a known astromolecule that may be ejected into the gas phase. HCCH and HCN bind to MgNC–nH2O to form intermediate radical compounds that may then also react with H atoms. There is enough reaction energy from H addition to eject fragments of the intermediates into the gas phase: the vinyl radical (C2H3) for HCCH and the methaniminyl radical (H2CN) for HCN. That leaves MgNC–nH2O to perform further catalytic activity. Alternatively, various hydrogenated divalent Mg compounds may also be stabilized and frozen into the ice or potentially ejected into the gas phase. Benchmark coupled cluster theory calculations in limited systems were used to characterize the submerged reaction barriers present when HCCH or HCN add to MgNC in the gas phase.

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Surface astrochemistry: a computational chemistry perspective

Cited by 3 publications

References 32 publications

Gas-dust chemistry of volatiles in the star and planetary system formation

Computer Generated Realistic Interstellar Icy Grain Models: Physicochemical Properties and Interaction with NH₃

Icy Grain Mantle Surface Astrochemistry of MgNC: The Emergence of Metal Ion Catalysis Studied via Model Ice Cluster Calculations

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Surface astrochemistry: a computational chemistry perspective

Cited by 3 publications

References 32 publications

Gas-dust chemistry of volatiles in the star and planetary system formation

Computer Generated Realistic Interstellar Icy Grain Models: Physicochemical Properties and Interaction with NH3

Icy Grain Mantle Surface Astrochemistry of MgNC: The Emergence of Metal Ion Catalysis Studied via Model Ice Cluster Calculations

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Computer Generated Realistic Interstellar Icy Grain Models: Physicochemical Properties and Interaction with NH₃