The Role of Radiolysis in the Modelling of C$_{2}$H$_{4}$O$_{2}$ Isomers and Dimethyl Ether in Cold Dark Clouds

TL;DR

This paper investigates how radiolysis, caused by cosmic rays, influences the formation and abundance of specific complex organic molecules in cold dark clouds, explaining observations of these molecules in such environments.

Contribution

It introduces a model incorporating radiolysis effects to better predict COMs abundances in cold dark clouds, addressing gaps in previous models.

Findings

Radiolysis significantly increases COMs production in ice mantles.

Model results align with observed abundances in TMC-1, L1689B, and B1-b.

Radiolysis explains the presence of COMs in cold environments.

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.