The microwave spectra of the following isotopic species of nitryl fluoride have been investigated and assigned: 14N16O2F,14N18O16OF, and 15N16O2F. Rotational constants from the three species have been used to determine the structure in several ways. The following structure is reported: ∠ ONO = 136°± 1·5°, rN–O= 1·1798 ± 0·0035 Å, rN–P= 1·467 ± 0·015 Å, and rO–O= 2·1878 ± 0·003 Å. The Stark effect of the 101â†� 000 transition of the 15N species has been studied and yields a dipole moment of 0·466 ± 0·005 D. A new method of preparing nitryl fluoride, which proved particularly convenient for the preparation of isotopically enriched species, has been developed.