Knowledge Bank

High resolution infrared spectra of the $\nu 1-\nu 2,\nu 3$ and $2\nu 2-\nu 2$ bands of $SO2$ reported $previously1.2$ have been recalibrated and reanalyzed using an Hamiltonian which accounts for weak interactions between the (020), (100) and (001) vibrational levels. In order to fit the observed data to within the experimental uncertainties, it was necessary to include a $\Delta K=2$ Fermi-type term to treat the interaction between the (020) and (100) states and a $\Delta K=3$ Coriolis-type term to treat the interactions between the two fundamental levels. Discrepancies noted by Vanek $etal.3$ between high precision heterodyne measurements on the $\nu 3$ band and predicted frequencies have been resolved. In addition, the $3\nu 3$ band has been refit using a perturbation treatment including a Fermi-like interaction term linking the (003) state with the (131) state resulting in more satisfactory estimates of several higher-order centrifugal distortion constants. With this improved data base, the rotational constants of 14 vibrational states have been fit to obtain a set of equilibrium rotational constants and rotation-vibration interaction constants. An improved equilibrium structure of the molecule has been obtained.