Observation of b$_2$ symmetry vibrational levels of the SO$_2$ $ ilde{\mbox{C}}$ $^1$B$_2$ state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants

摘要

The $\mathrm{\tilde{C}}$ $^1$B$_2$ state of SO$_2$ has a double-minimumpotential in the antisymmetric stretch coordinate, such that the minimum energygeometry has nonequivalent SO bond lengths. However, low-lying levels with oddquanta of antisymmetric stretch (b$_2$ vibrational symmetry) have notpreviously been observed because transitions into these levels from thezero-point level of the $\mathrm{\tilde{X}}$ state are vibronically forbidden.We use IR-UV double resonance to observe the b$_2$ vibrational levels of the$\mathrm{\tilde{C}}$ state below 1600 cm$^{-1}$ of vibrational excitation. Thisenables a direct characterization of the vibrational level staggering thatresults from the double-minimum potential. In addition, it allows us todeperturb the strong $c$-axis Coriolis interactions between levels of a$_1$ andb$_2$ vibrational symmetry, and to determine accurately the vibrationaldependence of the rotational constants in the distorted $\mathrm{\tilde{C}}$electronic state.