Low-energy electron-driven functionalization of benzene--water ices to phenol

Low-energy electrons abundantly generated by galactic cosmic radiation are expected to play a central role in the radiation chemistry of interstellar and cometary ices, yet their capacity to drive specific bond-forming reactions in simple aromatic systems remains poorly constrained. Here, sub-12 eV electrons were used to irradiate mixed benzene (C_6H_6)--water ices under cryogenic conditions, which led to the selective formation of phenol (C_6H_5OH) via C--O bond formation at the aromatic ring. Energy-resolved measurements show that the phenol yield is governed by resonant processes, consistently with dissociative electron attachment and electronically excited states of the condensed benzene--water matrix. Temperature-programmed desorption combined with mass-spectrometry diagnostics allowed the direct quantification of phenol production. These results demonstrate that low-energy electrons alone can promote net hydroxylation of benzene in icy environments, providing a previously underappreciated route to phenolic species in dense clouds, star-forming regions and irradiated icy bodies, and highlighting electron-induced functionalization as a key driver of aromatic complexity in astrochemical ices.