The rotational structure in twenty vibration rotation bands of 15N218O observed between 1080 and 4910 cm-1, has been measured and analyzed. In view of the improved resolution available, it has been possible to resolve many more l-type doublets than before. Three Fermi diads were measured, and from these data it was possible to establish an average value for the Fermi interaction parameter, k122 = 32.3 cm-1. Isotopic impurity bands due to 15N216O, 15N14N18O, 14N15N18O, and 15N217O were identified. An experimental value of the rotational constant for the ground vibrational state of 15N217O as B0000 = 0.39276 ± 0.00003 cm-1 was determined. © 1969.