The role of radiolysis in the modelling of C2H4O2 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 C2H4O2 isomers – methyl formate (HCOOCH3), glycolaldehyde (HCOCH2OH), and acetic acid (CH3COOH) – and a chemically similar molecule, dimethyl ether (CH3OCH3), in cold dark clouds. We then compare our modelled gaseous abundances with observed abundances in TMC-1, L1689B, and B1-b.

Collisional excitation and non-LTE modelling of interstellar chiral propylene oxide

“…Perhaps even more striking are the observations of COMs in the cold, dark starless core TMC-1 (see, e.g., Agúndez et al 2021), where the kinetic temperatures are well known to be substantially below the thermal desorption threshold. A number of physical and physiochemical processes have been theorized to account for the non-thermal desorption of COMs from grain surfaces (Paulive et al 2021), as well as substantial quantum chemical efforts suggesting potential new pathways for gas-phase formation (Balucani et al 2018). A generalized picture of these processes, and under what conditions they dominate, remains absent.…”

Precursors of the RNA-world in space: Detection of ($Z$)-1,2-ethenediol in the interstellar medium, a key intermediate in sugar formation

“…The chemistry of acetic acid, methyl formate and glycolaldehyde has been extensively discussed in several works (see e.g. Laas et al 2011;Burke et al 2015;Skouteris et al 2018;El-Abd et al 2019;Ahmad et al 2020;Mininni et al 2020;Paulive et al 2021).…”

Resolving desorption of complex organic molecules in a hot core

“…Moreover, observations of COMs in the absence of protostars in cold (T 20 K) regions, for example, the dark cloud TMC-1 (e.g., Agúndez et al 2021, and references therein) or prestellar cores (Bacmann et al 2012;Jiménez-Serra et al 2016, 2021Scibelli & Shirley 2020) but also in protostellar outflows such as L1157 (Codella et al 2015(Codella et al , 2017 and, for example, the shocked region (while quiescent in star formation) G+0.693−0.027 located in the Galactic centre region (e.g., Requena-Torres et al 2006;Zeng et al 2018), point to additional or purely non-thermal desorption processes. These processes may include grain-sputtering and subsequent release of COMs into the gas phase due to shock passing induced by outflows, accretion shocks (e.g., Csengeri et al 2019), or cloud interactions, desorption after interaction of molecules on dust grain surfaces with cosmic rays (Shingledecker et al 2018;Paulive et al 2021), or other diffusive and non-diffusive reactions taking place on the dust surface that lead to the chemical desorption of COMs (e.g, Ruaud et al 2015;Jin & Garrod 2020).…”

“…These processes may include grain-sputtering and subsequent release of COMs into the gas phase due to shock passing induced by outflows, accretion shocks (e.g. Csengeri et al 2019), or cloud interactions, desorption after interaction of molecules on dust grain surfaces with cosmic rays (Shingledecker et al 2018;Paulive et al 2021), or other diffusive and non-diffusive reactions taking place on the dust surface that lead to the chemical desorption of COMs (e.g, Ruaud et al 2015;Jin & Garrod 2020).…”