Knowledge Bank

All of the fundamentals of nitric acid have now been studied by high resolution infrared techniques. Additionally, the pure rotational spectrum of many of the excited states have been studied by millimeter/submillimeter spectroscopy. However, the analysis for many of the higher vibrational states are not complete. This is in part due to strong Fermi interactions involving interacting dyads such as $v5-2v9$ and $v3-v4$ which make the analysis much more complex. We have recently studied the $v5-2v9$ Fermi interacting bands which also involve torsional effects. The 2$v9$ torsional motion produces a large (~50 MHz) splitting. Since the 2$v9$ vibrational state interacts with the $v5$ vibrational state via Fermi resonance, a large splitting is also induced on the $v5$ energy levels. We have analyzed over 1000 rotational transitions from $v5-2v9$ using two models. The first uses 2 sets of 2$v9$ rotational constants and 1 set of $v5$ rotational constants coupled together by Fermi interactions, where a large Fermi term couples the torsional splitting from 2$v9$ to $v5$. The second uses a high barrier IAM approach to account for the torsional splitting. The results of both analyses will be presented as will preliminary results of higher vibrational states.