High-resolution laser-based one extreme-ultraviolet (EUV) +one UV two-photon ionization spectroscopy and EUV photoabsorption spectroscopy have been employed to study spin-forbidden Π3 u -X 1 g+ (v,0) transitions in N 14 2 and N 15 2. Levels of the C Π3 u valence and 3s g F3 and 3p π u G3 Π3 u Rydberg states are characterized, either through their direct optical observation, or, indirectly, through their perturbative effects on the Π1 u and 1 u+ states, which are accessible in dipole-allowed transitions. Optical observation of the G3 -X (0,0) and (1,0) transitions is reported for the first time, together with evidence for six new vibrational levels of the C state. Following the recent observation of the F3 -X (0,0) transition at rotational resolution [J. P. Sprengers et al., J. Chem. Phys. 123, 144315 (2005)], the F3 (v=1) level is found to be responsible for a local perturbation in the rotational predissociation pattern of the b′ 1 u+ (v=4) state. Despite their somewhat fragmentary nature, these new observations provide a valuable database on the Π3 u states of N2 and their interactions which will help elucidate the predissociation mechanisms for the nitrogen molecule. © 2008 American Institute of Physics.