AbstractReactivity toward low‐energy electrons (LEE) has been hypothesized as a cause of radio‐modifying properties for various molecules. LEE's transient nature, however, prevents the establishment of clear links between initial processes at the sub‐ps time scale and the final products of radiolysis. Here, such links are explored for the radio‐modifying compound RRx‐001 (1‐bromoacetyl‐3,3‐dinitroazetidine).Picosecond pulse radiolysis demonstrates the high scavenging capacity of the molecule for secondary quasi‐free and solvated electrons forming stable parent anions confirmed by studies of microsolvated RRx‐001 in clusters. The anions decay either via auto‐detachment of an electron or dissociate involving hydrogen transfer from solvent, resulting in NO2 and 1‐(bromoacetyl)‐3‐nitroazetidine. Surprisingly, no Br dissociation is observed despite its high electron affinity. We assign this behavior to the “inaccessibility” of sigma virtual states for electrons in the solvent, which can be of a general nature.