Absolute net nuclear polarization and their time dependencies are reported for the products of geminate and nongeminate radical ion pairs involved in the electron-transfer reaction between C-3(60) and the donor N,N-dimethyl-l-naphthylamine. Their analysis yields rate constants and reaction probabilities and shows that the electron back transfer between C60.- and D.+ is very efficient in benzonitrile/benzene. This is attributed to fast spin relaxation of C60.-.