Reactive Desorption and Radiative Association as Possible Drivers of Complex Molecule Formation in the Cold Interstellar Medium

TL;DR

This paper explores how reactive desorption and radiative association could drive the formation of complex organic molecules in the cold interstellar medium, challenging previous warm-up models and aligning with recent observations.

Contribution

It proposes a new gas-phase formation pathway involving reactive desorption and radiative association for complex molecules at very low temperatures.

Findings

Reactive desorption can produce complex organics at 10 K.

The scenario explains early-stage organic molecule abundances.

Results are mixed but promising for cold interstellar conditions.

Abstract

The recent discovery of terrestrial-type organic species such as methyl formate and dimethyl ether in the cold interstellar gas has proved that the formation of organic matter in the Galaxy begins at a much earlier stage of star formation than was thought before. This discovery represents a challenge for astrochemical modelers. The abundances of these molecules cannot be explained by the previously developed "warm-up" scenario, in which organic molecules are formed via diffusive chemistry on surfaces of interstellar grains starting at 30 K, and then released to the gas at higher temperatures during later stages of star formation. In this article, we investigate an alternative scenario in which complex organic species are formed via a sequence of gas-phase reactions between precursor species formed on grain surfaces and then ejected into the gas via efficient reactive desorption, a process in which non-thermal desorption occurs as a result of conversion of the exothermicity of chemical reactions into the ejection of products from the surface. The proposed scenario leads to reasonable if somewhat mixed results at temperatures as low as 10 K and may be considered as a step towards the explanation of abundances of terrestrial-like organic species observed during the earliest stages of star formation.