The charge transfer reaction of N-2(+)(v = 0-4) + Kr-->N-2+Kr+ is studied at thermal energy as a function of vibrational excitation in the reactant ion, The selected-ion flow tube technique coupled with laser-induced fluorescence detection is used to measure the vibrationally state specific rate constants. A dramatic vibrational enhancement is observed; measured rate constants are 1.0 (+/-0.6)x10(-12), 2.8 (+/-0.3)x10(-12), 2.1 (+/-0.2)x10(-11), 5.1 (+/-0.2)x10(-11), and 8.3 (+/-0.4)x10(-11) cm(3) molecule(-1) s(-1) for v=0, 1, 2, 3 and 4, respectively. Mass spectrometric kinetics experiments are also performed to confirm that vibrational relaxation, N-2(+)(v)+Kr-->N-2(+)(v’ < v) + Kr, is a negligible process. The charge transfer for v = 0 is extremely slow in spite of the large exothermicity (e.g., 0.915 eV for the production of N-2(v’ = 0)+Kr+(P-2(1/2)) states), yet the reaction is enhanced when the apparent energy mismatch is greater for the vibrationally excited reactant. A simple model is proposed to explain the experimental results at thermal energies (much less than 1 eV). The model assumes that only the most energy-resonant exothermic transitions, N-2(+)(v) + Kr-->N-2(v + 3)+Kr+(P-2(1/2)), occur within the duration of the ion-molecule collision complex and that the charge transfer takes place with probabilities governed by the corresponding Franck-Condon factors. However, the Franck-Condon factors are modified by a trial displacement of 0.02 Angstrom to account for the changes in vibrational wave functions of N-2(+) and N-2 during a close approach of the (N-2-Kr)(+) pair; this method gives an excellent description of the experimental results.