Isotopic analysis of stable nitrogen by the optic emission method has become quite widespread. As reported a few years ago, the 14N14N bandhead at 2977 Å and the 14N15N bandhead at 2983 Å constitute one of the best pairs for the spectral determination of the 15N abundance in nitrogen samples of low enrichment.
Victor Middelboe, "On Accuracy and Sensitivity in Optical 15N-Analysis," Appl. Spectrosc. 24, 608-609 (1970)