Knowledge Bank

The measurement and analysis of the rotational spectrum of nitric acid in the first three excited vibrational states above $1000cm-1$ will be presented. The assignments in each state involve transitions well into the asymmetric rotor limit with over 450 transitions measured in each state that span the frequency range from 80-525 GHz with quantum numbers ranging up to $J\sim 55$ and $Kc\sim 40$. The rotational transitions in the $7191$ and $6191$ states exhibit a $\sim 12$ MHz and $\sim 23$ MHz torsional splitting, respectively, requiring an internal axis system Hamiltonian with a set of torsional parameters to reproduce the observed spectra. There is no resolvable torsional splitting in the $72$ spectrum. Each state was fit separately and free from strong perturbations. The rms deviation of each analysis is close to the experimental uncertainty of $\sim 100$ kHz and the fitted rotational constants of each state agree well with those predicted from the ground, $61,71$, and $91$ states.