We examine radical mediated pathways in electrophilic addition to the simplest alkene, ethylene, where the structure of the radical intermediate has been extensively debated. Starting from the pi-complex with a dihalogen, C2H4 center dot center dot center dot I-2, isolated in an inert matrix, we initiate reaction by photolytically cleaving the I-2 bond. We succeed in trapping and spectroscopically interrogating the symmetrically bridged radical complex, which calculations confirm is the global minimum on the C2H5I Potential Energy Surface (PES). Consistent with the participation of a bridged intermediate, radical addition preferentially but not exclusively yields the anti-stereoisomer of the 1,2-diiodoethane product. (C) 2012 Published by Elsevier B.V.