The Δk = ±2 "forbidden band" and inversion–rotation energy levels of ammonia

An entire band of perturbation allowed transitions to the ν4 state of 14NH3 has been assigned in the Fourier transform spectra recorded using a 192-m path length. More than 900 of the forbidden transitions provide necessary information on the spacing between the energy levels with different quantum numbers k, inaccessible from allowed transitions. These data were combined with all other relevant data (MW, submillimetrewave, FIR, IR) published in the literature to derive precise values of inversion–rotation energy levels. This extensive data set completely describes the ground state energy levels of 14NH3 up to quantum number J = 16 for all possible values of the quantum number k.