Two-State Reactivity in the Rebound Step of Alkane Hydroxylation by Cytochrome P-450: Origins of Free Radicals with Finite Lifetimes This research was sponsored by the Israeli Science Foundation (ISF) and, in part, by the German Israeli Foundation (GIF), and the VW Stiftung. S.S. thanks the Humboldt Foundation for a Senior Research Award. F.O. thanks the EU for a Marie Curie Fellowship.