Formation of complex organic molecules on interstellar CO ices? Insights from computational chemistry simulations

Abstract

Carbon (${}^3$P) atom is a reactive species that, according to laboratory experiments and theoretical calculations, condensates with interstellar ice components. This fact is of uttermost importance for the chemistry in the interstellar medium (ISM) because the condensation reaction is barrierless and the subsequent species formed are still reactive given their open-shell character. Carbon condensation on CO-rich ices forms the \ch{C=C=O} (${}^3$$\Sigma$${}^{-}$) species, which can be easily hydrogenated twice to form ketene (H${}_2$CCO). Ketene is very reactive in terrestrial conditions, usually found as an intermediate hard to be isolated in chemical synthesis laboratories. These characteristics suggest that ketene can be a good candidate to form interstellar complex organic molecules (iCOMs) via a two-step process, i.e., its activation followed by a radical-radical coupling. In this work, reactions between ketene and atomic H, and the OH and NH${}_2$ radicals on a CO-rich ice model have been explored by means of quantum chemical calculations complemented by kinetic calculations to evaluate if they are favourable in the ISM. Results indicate that H addition to ketene (helped by tunneling) to form the acetyl radical (CH${}_3$CO) is the most preferred path, as the reactions with OH and NH${}_2$ possess activation energies ($\ge$ 9kJ/mol) hard to surmount in the ISM conditions, unless external processes provide energy to the system. Thus, acetaldehyde (CH${}_3$CHO) and, probably, ethanol (CH${}_3$CH${}_2$OH) formation via further hydrogenations are the possible unique operating synthetic routes. Moreover, from the computed relatively large binding energies of OH and NH${}_2$ on CO ice, slow diffusion is expected, hampering possible radical-radical couplings with CH${}_3$CO. The astrophysical implications of these findings are discussed considering the incoming James Webb Space Telescope observations.

References in corpus (21)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• An Ice Age JWST inventory of dense molecular cloud ices
• The origin of complex organic molecules in prestellar cores
• Binding energies: new values and impact on the efficiency of chemical desorption
• CORINOS I: JWST/MIRI Spectroscopy and Imaging of a Class 0 protostar IRAS 15398-3359
• The census of complex organic molecules in the solar type protostar IRAS16293-2422
• Reactivity of HCO with CH3 and NH2 on Water Ice Surfaces. A Comprehensive Accurate Quantum Chemistry Study
• Production of complex organic molecules: H-atom addition versus UV irradiation
• Formation of COMs through CO hydrogenation on interstellar grains
• Quantum mechanical simulations of the radical-radical chemistry on icy surfaces
• Quantum tunneling during interstellar surface-catalyzed formation of water: the reaction H + H${}_2$O${}_2$ $\to$ H${}_2$O + OH
• Atom Tunneling in the Water Formation Reaction H${}_2$ + OH $\to$ H${}_2$O + H on an Ice Surface
• A pathway to peptides in space through the condensation of atomic carbon
• Carbon Atom Reactivity with Amorphous Solid Water: H${}_2$O Catalyzed Formation of H${}_2$CO
• Hydrogenation of accreting C-atoms and CO molecules -- simulating ketene and acetaldehyde formation under dark and translucent cloud conditions
• Formation of Acetaldehyde on CO-rich Ices
• Influence of surface and bulk water ice on the reactivity of a water-forming reaction
• Behavior of Hydroxyl Radicals on Water Ice at Low Temperatures
• Dual-Level Approach to Instanton Theory
• Experimental Characterization of the Energetics of Low-temperature Surface Reactions
• A New "Non-energetic" Route to Complex Organic Molecules in Astrophysical Environments: The C + H${}_2$O $\to$ H${}_2$CO Solid-state Reaction

Cited by in corpus (8)

• Laboratory and Computational Studies of Interstellar Ices
• Enhanced formation of interstellar complex organic molecules on carbon monoxide ice
• Carbon Isotope Fractionation of Complex Organic Molecules in Star-Forming Cores
• Binding energies of ethanol and ethylamine on interstellar water ices: synergy between theory and experiments
• Hydrogenation of acetaldehyde on interstellar ice analogs reveals limited destruction
• Rate constants and product yields for the C + CH3CHO reaction at low temperatures
• Isotopomer-Specific Carbon Isotope Ratio of Complex Organic Molecules in Star-Forming Cores
• The Reaction between Atomic Carbon and Molecular Nitrogen as a Source of Cyanamide and Carbodiimide on Interstellar Ices