Observation of b2 symmetry vibrational levels of the SO2 (C)over-tilde 1B2 state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants

The (C) over tilde B-1(2) state of SO2 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(2) vibrational symmetry) have not previously been observed because transitions into these levels from the zero-point level of the (X) over tilde state are vibronically forbidden. We use IR-UV double resonance to observe the b(2) vibrational levels of the (C) over tilde state below 1600 cm(-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(1) and b(2) vibrational symmetry and to determine accurately the vibrational dependence of the rotational constants in the distorted (C) over tilde electronic state. (C) 2016 AIP Publishing LLC.