Knowledge Bank

The millimeter-wave spectrum of nitric acid ($HNO3$) in its $\nu 5$ and $2\nu 9$ vibrational states has been studied. Data were taken using a TWT based broadband spectrometer. The $\nu 5$ and $2\nu 9$ states exhibit a large perturbation from the ordinary Watson Hamiltonian due to a Fermi interaction between the energy levels. Additionally, the large torsional splitting of transitions following b-type selection rules was observed for the $2\nu 9$ vibrational state. An interesting effect arising from the mixing of the $2\nu 9$ and $\nu 5$ energy levels is the large splitting of the b-type transitions of the $\nu 5$ vibrational state. A smaller torsional splitting was observed for transitions following a-type selection rules inn the Q-branch transitions of both $\nu 5$ and $2\nu 9$. The results of our analysis will be presented and compared with the results of previous studies.