Formation of Complex Organic Molecules in Cold Interstellar Environments through Nondiffusive Grain-surface and Ice-mantle Chemistry

2020/06/19 by Mihwa Jin, Miwha Jin, Robin T. Garrod · 6 citations
Chemical Engineering · Physics and Astronomy · #Advanced Chemical Physics Studies #Advanced Combustion Engine Technologies #Astrochemistry #Astrophysics and Star Formation Studies #Chemical reaction #Desorption #Formate #Interstellar cloud #Interstellar medium #Methyl formate #Molecule #Photodissociation #Radical #astro-ph.GA #astro-ph.IM

paper · pdf · doi:10.3847/1538-4365/ab9ec8

43 pages, 15 figures, Accepted for publication in ApJS

arxiv created 2020/06/19 · openalex created_date 2020/06/25 · openalex publication_date 2020/08/01 · arxiv updated 2020/08/19 · openalex updated_date 2026/08/06

Abstract

Abstract A prevailing theory for the interstellar production of complex organic molecules (COMs) involves formation on warm dust-grain surfaces, via the diffusion and reaction of radicals produced through grain-surface photodissociation of stable molecules. However, some gas-phase O-bearing COMs, notably acetaldehyde (CH 3 CHO), methyl formate (CH 3 OCHO), and dimethyl ether (CH 3 OCH 3 ), are now observed at very low temperatures, challenging the warm scenario. Here, we introduce a selection of new nondiffusive mechanisms into an astrochemical model to account for the failure of the standard diffusive picture and to provide a more generalized scenario of COM formation on interstellar grains. New generic rate formulations are provided for cases where (i) radicals are formed by reactions occurring close to another reactant, producing an immediate follow-on reaction; (ii) radicals are formed in an excited state, allowing them to overcome activation barriers to react with nearby stable molecules; and (iii) radicals are formed through photodissociation close to a reaction partner, followed by immediate reaction. Each process occurs without thermal diffusion of large radicals. The new mechanisms significantly enhance cold COM abundances, successfully reproducing key observational results for prestellar core L1544 . H abstraction from grain-surface COMs, followed by recombination, plays a crucial role in amplifying chemical desorption into the gas phase. The ultraviolet-induced chemistry produces significant COM abundances in the bulk ices, which are retained on the grains and may persist to later stages. O 2 is also formed strongly in the mantle though photolysis, suggesting cometary O 2 could indeed be interstellar.

Citations

• Complex Chemistry in Star‐forming Regions: An Expanded Gas‐Grain Warm‐up Chemical Model
• Evidence for Extraterrestrial Amino-acids and Hydrocarbons in the Murchison Meteorite
• DETECTION OF THE SIMPLEST SUGAR, GLYCOLALDEHYDE, IN A SOLAR-TYPE PROTOSTAR WITH ALMA
• Observations of the Icy Universe
• Modelling complex organic molecules in dense regions: Eley–Rideal and complex induced reaction
• Cometary glycine detected in samples returned by Stardust
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Complex Organic Interstellar Molecules
• A primordial origin for molecular oxygen in comets: a chemical kinetics study of the formation and survival of O2ice from clouds to discs
• Formation of Complex Molecules in Prestellar Cores: A Multilayer Approach
• Chemical complexity induced by efficient ice evaporation in the Barnard 5 molecular cloud

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• Tracking the dynamical, chemical and spectral evolution of molecular cores with PrestaLine: Gorynych
• Using astrochemical models to simulate reactivity experiments on cold surfaces
• CO Diffusion on Interstellar Amorphous Solid Water: A Computational Study
• Methanol Formation via the Radical-radical Reaction of OH and CH3 Radicals Undergoing Transient Diffusion on Ice at 10 to 60 K
• The role of radiolysis in the modelling of C2H4O2 isomers and dimethyl ether in cold dark clouds