- Abstract In recent years, sophisticated diabatic Hamiltonians have been developed in order to understand the low-energy vibronic level structure of the nitrate radical (NO_3), which exhibits strong coupling between the~ X and doubly degenerate~ B states. Previous studies have reproduced the observed vibronic level positions up to 2000 wn~ above the zero-point level, yet the rotational structure has remained uninvestigated with ab initio methods. In this talk, we present calculations of the N>= 0 rovibronic structure of low-lying vibronic states of NO_3, in which complicated rovibrational and Coriolis interactions have been observed. Our results include calculations using both adiabatic and diabatic Hamiltonians, enabling a direct comparison between the two. We discuss extensions of our treatment to include spin- orbit and spin-rotation effects.