The dynamics of proton transfer within a variety of substituted benzophenone-triethylamine triplet contact radical ion pairs are examined in the solvents acetonitrile and dirnethylformamide. The correlation of the proton-transfer rate constants with Delta G reveals an inverted region. The kinetic deuterium isotope effects are also examined. The solvent and isotope dependence of the transfer processes are analyzed within the context of the Lee-Hynes model for nonadiabatic proton transfer. Theoretical analysis of the experimental data suggests that the reaction path for proton/deuteron transfer involves tunneling, and the origin of the inverted region is attributed to a curved tunneling path.