When a molecule dissociates, three types of transport phenomena compete with recombination of the fragments. Translational diffusion carries the cleavage products into the bulk medium, diluting them so that reencounters steadily become less probable with time. Heat conduction equilibrates the energies of the products with that of the medium, dissipating any excess energy left over from surmounting an activation barrier. Finally, rotational diffusion washes out the angular correlations dictated by the transition state. At the instant a bond is broken the fragments point toward one another in a way that is most conducive to re-forming the bond. The memory of this nascent relative orientation is soon lost as the fragments start to rotate independently of each other. This is portrayed schematically in eq 1. D a d McAdoo grew up in westem Pennsylvania, recelved his bachelor's degree from Lafayette Corkge and hls Ph.D. from Comell Unlverslty (wlth F. W. McLafferty), and dld po&doctml work at Johns Hopklns Unlverslty. He has been employed by the USDA, U n h Carblde, and Jet Ropulsbn Laboratory, and he ls currently a " b r of the Marine Bbmdical Institute and professor of human bkbglcal chemistry and genetics, cellular physiobgy and membrane bkphydcs, and nwocrcknces at the University of Texas Medlcal Branch at Qahton. Other sdentlflc Interests are neurochemistry and neurophyslology. Nonprofeaslonal Intere8ta Include the exploratbn of caves. Tom Morton waa bom In Loo Angebs, where his forebears (both Hellman and Morton) were employed by the motion pichrre Industry. He recelved h18 AB from Haward In 1968 In clas.sks (&e&) and flne arts and his Ph.D. from Cattech under the joht dbctbn of R. Q. Bergman and J. L. Beauchamp. Since 0 1993 American Chemical Society (14) (a) Audier, H. E.; Milliet, A.; Leblanc, D.; Morton, T. H. J. Am. Chem. SOC. 1992,114,2020-2027. (b) Cao, J. R.; George, M.; Holmes, J. L.; Siroie, M.; Terlouw, J. K.;Burgers, P. C. J. Am. Chem. SOC. 1992,114, (15) Postma, R.; Ruttink, P. J. A.; van Baar, B. L. M.; Terlouw, J. K.; Holmes, J. L.; Burgers, P. Chem.