CARS AND INFRARED STUDIES OF $^{32}S^{16}O_{3}$: HOW CAN SUCH A SIMPLE MOLECULE GIVE SUCH A COMPLEX SPECTRUM?

Author Institution: Department of Chemistry, Oregon State University; National Science Foundation, National Institute of Standards and Technology; National Science Foundation, Pacific Northwest National LaboratorySulfur trioxide is an important participant in reactions in the upper atmosphere and also in a number of industrial processes. It is a $D_{3h}$ planar oblate top whose spectroscopy is surprisingly incomplete, in part due to its extreme corrosive properties. We report here a comprehensive investigation of all four fundamental bands of $^{32}S^{16}O_{3}$. High resolution ($0.001 cm^{-1}$) coherent anti-Stokes Raman scattering (CARS) has been used at Oregon State University to examine the Q-branch structure of the IR-inactive $\nu_{1}$ symmetric stretching mode of $^{32}S^{16}O_{3}$. This spectrum reveals two intense Q-branch regions, with complex vibrational-rotational structure. The modeling of this has been challenging and involves a subtle combination of Fermi-resonances, indirect Coriolis interactions, and l-resonances with nearby hidden states; $2\nu_{4} (l=0, \pm 2),\nu_{2} + \nu_{4} (l = \pm 1), 2\nu_{2} (l=0)$. The analysis of the perturbed $\nu_{1}$ spectrum, achieved by locating these states via high-resolution infrared hot-band studies performed at Pacific Northwest National Laboratory, will be presented in this talk