Experimental evidence for Glycolaldehyde and Ethylene Glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions

TL;DR

This paper provides experimental evidence that glycolaldehyde and ethylene glycol can form through surface hydrogenation of CO molecules in dense molecular clouds, with implications for astrochemical models.

Contribution

It demonstrates experimentally that complex molecules like glycolaldehyde and ethylene glycol form via CO hydrogenation, and integrates these pathways into astrochemical models.

Findings

Formation of glycolaldehyde and ethylene glycol confirmed experimentally.

Reaction pathways involving HCO radical recombination established.

Model predicts significant abundances of these molecules in dense clouds.

Abstract

This study focuses on the formation of two molecules of astrobiological importance - glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) - by surface hydrogenation of CO molecules. Our experiments aim at simulating the CO freeze-out stage in interstellar dark cloud regions, well before thermal and energetic processing become dominant. It is shown that along with the formation of H2CO and CH3OH - two well established products of CO hydrogenation - also molecules with more than one carbon atom form. The key step in this process is believed to be the recombination of two HCO radicals followed by the formation of a C-C bond. The experimentally established reaction pathways are implemented into a continuous-time random-walk Monte Carlo model, previously used to model the formation of CH3OH on astrochemical time-scales, to study their impact on the solid-state abundances in dense interstellar clouds of glycolaldehyde and ethylene glycol.