Electron-induced chemistry is relevant to many processes that occur when ionizing radiation interacts with matter. This includes radiation damage, curing of polymers, and nanofabrication processes but also the formation of complex molecules in molecular ices grown on dust particles in space. High-energy radiation liberates from such materials an abundance of secondary electrons of which most have energies below 20 eV. These electrons efficiently trigger reactions when they attach to molecules or induce electronic excitation and further ionization. This review focuses on the present state of insight regarding the mechanisms of reactions induced by electrons with energies between 0 and 20 eV that lead to formation of larger products in binary ice layers consisting of small molecules (H2O, CO, CH3OH, NH3, CH4, C2H4, CH3CN, C2H6) or some derivatives thereof (C2H5NH2 and (C2H5)2NH, CH2=CHCH3). It summarizes our approach to identify products and quantify their amounts based on thermal desorption spectrometry (TDS) and electron-stimulated desorption (ESD) experiments performed in ultrahigh vacuum (UHV). The overview of the results demonstrates that, although the initial electron-molecule interaction is a non-thermal process, product formation from the resulting reactive species is often governed by subsequent reactions that follow well-known thermal and radical-driven mechanisms of organic chemistry.

Chemical reactions in mixed molecular ices as relevant in the context of astrochemistry can be initiated by electron-molecule interactions. Dissociative electron attachment (DEA) as initiating step is identified from the enhancement of product yields upon irradiation at particular electron energies. Herein, we show that DEA to CO leads to the formation of HCN in mixed CO/$$\hbox {NH}_{{3}}$$ NH 3 ice at electron energies around 11 eV and 16 eV. We propose that this reaction proceeds via insertion of the neutral C fragment into a N–H bond. In the case of CO/$$\hbox {H}_{{2}}$$ H 2 O and CO/$$\hbox {CH}_{{3}}$$ CH 3 OH ices, a resonant enhancement of the yields of HCOOH and $$\hbox {CH}_{{3}}$$ CH 3 OCHO, respectively, is observed around 10 eV. In both ices, both molecular constituents exhibit DEA processes in this energy range so that the energy-dependent product yield alone does not uniquely identify the relevant DEA channel. However, we demonstrate by comparing with earlier results on mixed ices where CO is replaced by $$\hbox {C}_{{2}}\hbox {H}_{{4}}$$ C 2 H 4 that DEA to CO is again responsible for the enhanced product formation. In this case, $$\hbox {O}^{\cdot -}$$ O · - activates $$\hbox {H}_{{2}}$$ H 2 O or $$\hbox {CH}_{{3}}$$ CH 3 OH which leads to the formation of larger products. We thus show that DEA to CO plays an important role in electron-induced syntheses in molecular ices. Graphical abstract

This article unfortunately contains mistakes that were made by the typesetter when incorporating corrections noted by the authors. The correct formula and citations are as follows:Section 3.1: On page 4, the correct citations must read '...enhanced around 12 eV [34,35]...' and '...evinces a second resonance around 16 eV [34,35].' The correct spelling of the radical anion is O •− .