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

Abstract

Hamiltonian in the Fermi-system basis, the vibrational characters of all vibrational levels can be determined unambiguously. It is shown that the bending mode cannot be treated separately from the coupled stretching modes, particularly at vibrational energies of more than 2000 cm −1 . Based on our force field, the structure of the Coriolis interactions in theC state of SO 2 is also discussed.We identify the origin of the alternating patterns in the effective C rotational constants of levels in the vibrational progressions of the symmetry-breaking mode, ν β (which correlates with the antisymmetric stretching mode in our assignment scheme).

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

“…force field. 9 The C constants of (0,1,0) and (0,0,1) are, respectively, higher and lower than the observed trends, partly because of a Coriolis interaction that we have not deperturbed, due to the lack of high-J data from (0,0,1) necessary to make a precise determination of the inter- action. (The energy denominator is approximately 165 cm −1 .)…”

“…We obtain the value of ∆ vib from our force field fit, described in Part II of this series. 9 We ignore effects from the interaction of (0,1,1) with (0,2,0) because the energy denominator is large (∼170 cm −1 ) and is not expected to make a significant contribution to the low-lying rotational energy levels that we observe. The resulting fit, given in Table III, to a com- Table S.II of the supplementary material).…”

“…The degree of staggering increases as quanta of v 2 are added, but decreases when one quantum of v 1 is added. The vibrational level structure will be discussed in detail in parts II and III of this series, where we report a new C-state force field 9 and discuss the mechanism of the vibronic distortions. 11…”

“…In this part, we report the staggered vibrational energy levels of the SO 2 C state, we perform a rotational analysis of the strong c-axis Coriolis interactions, and we determine the rotational constants and rotation-vibration constants. In part II of the series, 9 we fit the available data on the C state (including rotational constants, rovibrational information, and isotopologue data) to an internal coordinate force field model. Using a two-step diagonalization procedure, we characterize a large number of highly mixed levels below 3000 cm −1 of vibrational excitation, and we calculate the anharmonic Franck-Condon factors for the C ← X absorption spectrum.…”

The origin of unequal bond lengths in the C̃1B2 state of SO2: Signatures of high-lying potential energy surface crossings in the low-lying vibrational structure

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] However, earlier spectroscopy by Duchesne and Rosen 16 , Jones and Coon 17 , Brand and coworkers 18,19 , and by Hallin and Merer 20 focussed on the unusual low-lying vibrational structure below the dissociation limit, which was apparently the result of a distortion causing unequal SO bond lengths at the minimum-energy geometry. In the first paper of this series, 21 we report the first direct observations ofC-state levels with b 2 vibrational symmetry (odd quanta of v 3 ), and in the second paper, 22 we report a new force field. This new information provides us with the opportunity to make a more precise characterization of the origins of level staggering than was previously possible.…”