The Role of Radiolysis in the Modelling of C${}_2$H${}_4$O${}_2$ Isomers and Dimethyl Ether in Cold Dark Clouds

Abstract

Complex organic molecules (COMs) have been detected in a variety of interstellar sources. The abundances of these COMs in warming sources can be explained by syntheses linked to increasing temperatures and densities, allowing quasi-thermal chemical reactions to occur rapidly enough to produce observable amounts of COMs, both in the gas phase, and upon dust grain ice mantles. The COMs produced on grains then become gaseous as the temperature increases sufficiently to allow their thermal desorption. The recent observation of gaseous COMs in cold sources has not been fully explained by these gas-phase and dust grain production routes. Radiolysis chemistry is a possible non-thermal method of producing COMs in cold dark clouds. This new method greatly increases the modeled abundance of selected COMs upon the ice surface and within the ice mantle due to excitation and ionization events from cosmic ray bombardment. We examine the effect of radiolysis on three C${}_2$H${}_4$O${}_2$ isomers -- methyl formate (HCOOCH${}_3$), glycolaldehyde (HCOCH${}_2$OH), and acetic acid (CH${}_3$COOH) -- and a chemically similar molecule, dimethyl ether (CH${}_3$OCH${}_3$), in cold dark clouds. We then compare our modelled gaseous abundances with observed abundances in TMC-1, L1689B, and B1-b.

arXiv comment12 pages, 6 Figures, 5 tables, 33 numbered equations

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• Shocking Sgr B2(N1) with its own outflow: A new perspective on segregation between O- and N-bearing molecules
• On Modelling Sputtering of Interstellar Grain Ices
• Carbon-Chain Chemistry vs. Complex-Organic-Molecule Chemistry in Envelopes around Three Low-Mass Young Stellar Objects in the Perseus Region
• Collisional excitation and non-LTE modelling of interstellar chiral propylene oxide
• Infrared action spectroscopy as tool for probing gas-phase dynamics: Protonated Dimethyl Ether, (CH${}_3$)${}_2$OH${}^{+}$, formed by the reaction of CH${}_3$OH${}_2^{+}$ with CH${}_3$OH
• Precursors of the RNA-world in space: Detection of ($Z$)-1,2-ethenediol in the interstellar medium, a key intermediate in sugar formation
• Simulation of proton radiolysis of H2O and O2 ices with the Nautilus code