The nf Rydberg levels of N-14(2) converging to the X (2) Sigma(g)(+) ground state of N-2(+) have been studied from n=4-9 in the high-resolution absorption spectra of supersonically expanding nitrogen at wavelengths ranging from 843.2 to 802.6 Angstrom (118 600-124 600 cm(-1)). The best experimental results, achieving rotational temperatures on the order of 20 to 40 K and a resolution of 0.5 cm(-1), were obtained by photographing the jet absorption against the background continuum from a synchrotron radiation source. Complementary data for N-14(2) and N-15(2) come from the analyses of spectra recorded under equilibrium conditions at 70 K with a resolution of 1 cm(-1), using the He continuum as background source. The observations are interpreted with the help of multichannel quantum defect calculations and lead to the conclusion that, to varying degrees and with the exception of 4f(v=0), all the complexes studied here show the effects of interactions with core excited d and s Rydberg levels built on the A (IIu)-I-2 first excited state of N-2(+). Also, the 9f(v=0) complex is shown to be perturbed by 10p(v=0), and the strength of the p-f interaction, has been determined.