Observation of b2 symmetry vibrational levels of the SO2 C̃ 1B2 state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants

The [~ over C] [superscript 1]B[subscript 2] state of SO[subscript 2] has a double-minimum potential in the antisymmetric stretch coordinate, such that the minimum energy geometry has nonequivalent SO bond lengths. However, low-lying levels with odd quanta of antisymmetric stretch (b[subscript 2] vibrational symmetry) have not previously been observed because transitions into these levels from the zero-point level of the [~ over X] state are vibronically forbidden. We use IR-UV double resonance to observe the b[subscript 2] vibrational levels of the [~ over C] state below 1600 cm[superscript −1] of vibrational excitation. This enables a direct characterization of the vibrational level staggering that results from the double-minimum potential. In addition, it allows us to deperturb the strong c-axis Coriolis interactions between levels of a[subscript 1] and b[subscript 2] vibrational symmetry, and to determine accurately the vibrational dependence of the rotational constants in the distorted [~ over C] electronic state