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

Abstract

The C̃ (1)B2 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 (b2 vibrational symmetry) have not previously been observed because transitions into these levels from the zero-point level of the X̃ state are vibronically forbidden. We use IR-UV double resonance to observe the b2 vibrational levels of the C̃ 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 a1 and b2 vibrational symmetry and to determine accurately the vibrational dependence of the rotational constants in the distorted C̃ electronic state.

The rotation-vibration structure of the SO2 C̃1B2 state explained by a new internal coordinate force field

“…Note that the three states are labeled according to the notations used in our CCPT-MODR paper on theC state, 26 Note that only the first eight b 2 vibrational symmetry levels have been experimentally observed in the IR-UV double resonance experiment. 25 This means that there is a large energy gap between the last observed b 2 level at 1595 cm −1 and this level at 2753 cm −1 .…”

“…However, accurate deperturbation had been impossible until the recent direct observation of b 2 vibrational levels. 25,26 In this section, we present level-specific Coriolis interaction strengths derived from our force field, and we analyze how the doublewell structure of the PES leads to specific diagnostic patterns of Coriolis interactions in thẽ C state.…”

“…data points for most of the observed vibrational levels, approximations must be made in the Coriolis fit, 25 in order to reduce correlations among the fit parameters. However, the general agreement between the experimental and calculated values supports the validity of these approximations.)…”

“…In addition to extensive anharmonic interactions, the majority of theC state vibrational levels exhibit c-axis Coriolis perturbations. 3,10,11,25,34 Since the effects of Coriolis interactions are sensitive to the energy spacings between levels, a double-well structure on the PES, which gives rise to vibrational level-staggerings, is expected to cause staggering-related anomalies in the rotational structure of theC state, especially in the vibrational levels that involve the symmetry-breaking mode. However, rotational information for levels with odd quanta of excitation in the symmetry-breaking mode had not been available until our recent direct observations of b 2 vibrational symmetry levels, reported in the first paper of this series 25 and in Ref 26. With those crucial pieces of information on the rotational structure of thẽ C state, we can now validate and interpret the rotational anomalies caused by the doublewell structure on the PES.…”

Final State Resolved Quantum Predissociation Dynamics of SO2(C̃1B2) and Its Isotopomers via a Crossing with a Singlet Repulsive State

“…[21][22][23] The spectroscopy of this so-called C band has been extensively studied in the past, and a plethora of spectroscopic data exist above the band origin at 42573 cm -1 . [24][25][26][27] Above 218 nm, SO2 is known to predissociate, as evidenced by a sudden decrease of fluorescence and broadening of the spectral features. 21,24,[28][29][30][31][32][33] The dissociation dynamics to the SO( 3 X   ) and O( 3 P) species has been studied by a number of groups, using different experimental techniques.…”