The complexity of the spectral region 3500–5500 Å has been noted in an earlier study and is due to the presence of many vibrational and rotational perturbations. New data which have been obtained, in particular from a complete study of the spectrum of 15N80Se, have led us to re-examine thoroughly our interpretation of the 3300–5800 Å region. We have thus arrived at a new vibrational assignment and have found evidence for two perturbing states: the b(4Σ−) state for which a transition to one level has been observed weakly and analyzed; the a (4Πi) state which has been identified and for which we have been able to determine vibrational and rotational constants. The relative position of the six observed states may be accounted for in terms of energy level and potential energy curve diagrams.