Complex Organic Molecules Formation in Cold Cores on Stochastically Heated Grains

TL;DR

This study explores how stochastic heating of dust grains influences the formation of complex organic molecules in cold interstellar cores, revealing the significance of grain size and coagulation effects on chemical evolution.

Contribution

It introduces a chemical model that incorporates stochastic grain heating and coagulation, providing new insights into COM formation in cold cores.

Findings

Grain coagulation affects gas-phase species like CO2 and N2H+.

Grains around 4.6×10^-3 μm are most effective for COM production.

Stochastic heating of grains helps explain observed COM abundances.

Abstract

We investigate the roles of stochastic grain heating in the formation of complex organic molecules (COMs) in cold cores, where COMs have been detected. Two different types of grain-size distributions are used in the chemical models. The first one is the MRN distribution, and the second one considers grain coagulation to study its effects on the chemical evolution in these environments. The macroscopic Monte Carlo method is used to perform the two-phase chemical model simulations. We find that (1) grain coagulation can affect certain gas-phase species, such as CO$_2$ and N$_2$H$^+$, in the cold core environments, which can be attributed to the volatile precursors originating from the small grains with temperature fluctuations; (2) grains with radii around 4.6 $\times$ 10$^{-3}$ $\mu$m contribute most to the production of COMs on dust grains under cold core conditions, while few species can be formed on even smaller grains with radii less than 2 $\times$ 10$^{-3}$ $\mu$m; (3) COMs formed on stochastically heated grains could help explain the observed abundances of gas-phase COMs in cold cores.