Picosecond dynamics of intermolecular proton and deuteron transfer between benzophenone and N,N-dimethylaniline

Picosecond absorption spectroscopy is used to study the dynamics of proton and deuteron transfer in the benzophenone/N,N-dimethylaniline contact radical ion pair in the solvents benzene and tetrahydrofuran. From temperature-dependent studies of this kinetic process, the energy of activation and A factors for proton and deuteron transfer are derived. These parameters are then analyzed within the classical and semiclassical models for proton transfer, the Borgis-Hynes model for proton transfer, and the two-step model developed by Kreevoy and Kotchevar for hydride transfer. We conclude that prior to proton transfer there is a rate-limiting reorganization of the contact radical ion pair complex that allows for the transfer of the proton.