Genesis of Polyatomic Molecules in Dark Clouds: CO$_2$ Formation on Cold Amorphous Solid Water

TL;DR

This study uses molecular dynamics simulations to investigate how CO$_2$ molecules form and stabilize on amorphous solid water surfaces in cold interstellar clouds, revealing rapid formation and long-term adsorption processes.

Contribution

It introduces a detailed simulation approach with high-quality potential energy surfaces to elucidate CO$_2$ formation mechanisms on icy dust grains in space.

Findings

CO$_2$ forms within sub-nanoseconds upon collision

CO$_2$ remains adsorbed on amorphous water ice over extended periods

Formation involves stabilization into CO$_2$ and COO molecules

Abstract

Understanding the formation of molecules under conditions relevant to interstellar chemistry is fundamental to characterize the chemical evolution of the universe. Using reactive molecular dynamics simulations with model-based or high-quality potential energy surfaces provides a means to specifically and quantitatively probe individual reaction channels at a molecular level. The formation of CO$_2$ from collision of CO($^1 \Sigma$) and O($^1$D) is characterized on amorphous solid water (ASW) under conditions typical in cold molecular clouds. Recombination takes place on the sub-nanosecond time scale and internal energy redistribution leads to stabilization of the product with CO$_2$ remaining adsorbed on the ASW on extended time scales. Using a high-level, reproducing kernel-based potential energy surface for CO$_2$, formation into and stabilization of CO$_2$ and COO is observed.