The autoionizing (X 2Σg+) 8ƒ, 9ƒ, and 10ƒ, v=1 states of N2 have been studied by using double-resonance ionization spectroscopy via numerous rotational levels of the a 1Πg, v´=5 state. These nƒ states lie in a complex region of the spectrum that also contains transitions to high vibrational levels of the b´ 1Σu+ valence state and Rydberg states that converge to the X 2Σg+, A 2Πu, and B 2Σu+ states of the ion. A long-range interaction model, which is based on the interaction of the Rydberg electron with the polarizability and quadrupole moment of the N2+ ion core, has been used to interpret the ƒ-state structure and to identify the extent of perturbations due to interactions with nearby states. A generalized least-squares fit of the model to the energies of the unperturbed 8ƒ state yields an effective quadrupole moment of (3.2±0.1)ea02 and an isotropic polarizability of (16.1±0.4)a03 for the X 2Σg+, v+=1 state of the ion. In addition, a new state that is observed to perturb the 9ƒ, v=1 state is tentatively identified as the previously unobserved (A 2Πu)3dπ 1Δu, v=2 state. The results presented here complete the interpretation of the single-photon absorption spectrum of N2 from the first ionizationmore » potential at ~ 125 667 to ~ 126 850 cm-1.« less