The high-resolution rotational spectrum of H 15 NO 3 has been recorded in the range between 74 and 850GHz and used to complete an extensive analysis of the six vibrational states below 1000cm −1 that include the isolated 8 1 and 9 1 states along with the weakly interacting 6 1 and 7 1 states and strongly interacting 5 1 and 9 2 dyad. The 6 1 and 7 1 states couple via a weak Coriolis interaction while the 5 1 and 9 1 states couple through strong Fermi and weaker Coriolis interactions. The Hamiltonian models account for the observed torsional splitting in the 9 1 and 9 2 states of 2.4 and 70MHz, respectively, and the induced torsional spitting of 15MHz in the 5 1 state due to the strong Fermi mixing with the 9 2 state. The transitions from each state are fit to within the experimental accuracy and the resulting spectroscopic constants agree well with the main isotopologue.