Modeling Complex Organic Molecules Formation in Cold Cores: Multi-phase Models with Non-thermal Mechanisms

TL;DR

This study develops multi-phase gas-grain models incorporating non-thermal mechanisms to better explain the formation of oxygen-bearing complex organic molecules in cold dark clouds, aligning well with astronomical observations.

Contribution

It introduces a novel multi-phase modeling approach with non-thermal processes, improving the understanding of COM formation in cold interstellar environments.

Findings

Models agree with observations within a factor of 3 for key molecules.

67% of species show agreement within one order of magnitude.

Non-thermal mechanisms significantly enhance model accuracy.

Abstract

In recent years, a significant number of oxygen-bearing complex organic molecules (COMs) have been detected in the gas phase of cold dark clouds such as TMC-1. The formation of these COMs cannot be explained by diffusive mechanisms on grains and gas phase reactions. This study investigates the formation of oxygen-bearing COMs in cold dark clouds using multiphase gas-grain models that incorporate cosmic ray-induced non-diffusive radiation chemistry and non-thermal sputtering desorption mechanisms. Additionally, we present the effects of varying elemental C/O ratio and different sputtering rates. We utilized an accelerated Gillespie algorithm, based on the regular Gillespie algorithm. The results of our models for dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), acetaldehyde (CH3CHO), ethanol (C2H5OH), and methanol (CH3OH) show reasonable agreement with observations toward TMC-1, within a factor of 3. Out of the 94 species compared with observations, 63 show agreement within 1 order of magnitude, accounting for 67.02%. Overall inclusion of non-thermal mechanisms in multi-phase models shows notable improvement of modeling on oxygen-bearing COMs in the interstellar medium.