Atom addition reactions in interstellar ice analogues

TL;DR

This review summarizes laboratory studies of atom addition reactions in interstellar ice analogues, highlighting formation pathways of water, carbon dioxide, methanol, and complex prebiotic molecules at low temperatures relevant to star formation.

Contribution

It compiles and discusses recent experimental data on reaction rates, mechanisms, and constants crucial for astrochemical modeling of interstellar ices.

Findings

Water, CO2, and methanol form in ices at low temperatures.

Formation of hydroxylamine and glycolaldehyde demonstrated.

Reaction parameters like barrier heights and rates are quantified.

Abstract

This review paper summarizes the state-of-the-art in laboratory based interstellar ice chemistry. The focus is on atom addition reactions, illustrating how water, carbon dioxide and methanol can form in the solid state at astronomically relevant temperatures, and also the formation of more complex species such as hydroxylamine, an important prebiotic molecule, and glycolaldehyde, the smallest sugar, is discussed. These reactions are particularly relevant during the dark ages of star and planet formation, i.e., when the role of UV light is restricted. A quantitative characterization of such processes is only possible through dedicated laboratory studies, i.e., under full control of a large set of parameters such as temperature, atom-flux, and ice morphology. The resulting numbers, physical and chemical constants, e.g., barrier heights, reaction rates and branching ratios, provide information on the molecular processes at work and are needed as input for astrochemical models, in order to bridge the timescales typical for a laboratory setting to those needed to understand the evolutionary stages of the interstellar medium. Details of the experiments as well as the astrochemical impact of the results are discussed.