The rotational spectra of the 7191, 6191, and 72 vibrational states of nitric acid

The rotational spectra of the first three vibrational states of nitric acid above 1000 cm−1, 7191, 6191, and 72, have been measured and analyzed. The 72 state, along with the previously published 71 state, show the rotational and centrifugal distortional constants have a near linear dependence on the υ7 vibrational quantum number. Large changes for several centrifugal distortion constants of the υ7 = n series of states are attributed to a c-type Coriolis resonance manifold between the ν7 and ν6 vibrational modes and the Hamiltonian reduction and representation used to fit the spectra. The 7191 and 6191 states have torsional splittings of 12.361(8) and 22.47(1) MHz, respectively. These splittings are large compared to 2.340(8) MHz of the 91 state and can be explained by a ∼1-2% mixing through anharmonic Fermi resonances with the 93 state, which has a large torsional splitting of ∼1760 MHz. The millimeter/submillimeter-wave spectrum of each state was fit separately to the experimental uncertainty of the measurements. The resultant rotational constants, distortional constants and inertial defects agree well with DFT calculations.