Uranyl Photochemistry with Alkenes: Distinguishing between H-Atom Abstraction and Electron Transfer We have studied the quenching of the uranyl ion in aqueous acetonitrile with a series of alkenes. The quenching rate constant (k(q)) increases linearly with decreasing ionization potential (IP) for a series of hexene isomers, as seen in a plot of In (k(q)) vs IP; no correlation is observed between the quenching rate and the bond dissociation energy of the allylic C-H bond. These results demonstrate that the mechanism of quenching for alkenes is electron transfer from the alkene to uranyl.