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We are engaged in a comprehensive investigation of the fundamental and low lying combination and overtone bands of the parent $^{32}S^{16}O_{3}$ as well as the $^{34}S^{16}O_{3}$, $^{32}S^{18}O_{3}$, and $^{34}S^{18}O_{3}$ isotopic variants of sulfur trioxide. CARS spectroscopy of the $\nu_{1}$ Raman active bands has been performed at Oregon State University and high resolution infrared absorption spectroscopy of room temperature static cell samples has been performed at PNNL using a Bruker IFS 120 HR Fourier transform spectrometer. Results for the absorption spectrum of the $2\nu_{3}$ band of $^{32}S^{16}O_{3}$, recorded at a resolution of $0.0025 cm^{-1}$, will be presented. The overtone of the $\nu_{3}$ fundamental $[(e^{\prime})^{2} = A^{\prime}_{1} + E^{\prime}]$ is centered at $2777.87139(5) cm^{-1}$ with $B^{\prime} = 0.3462802(2) cm^{-1}$ and $B^{\prime\prime} = 0.34854336(4) cm^{-1}$. Assignment and fitting of the perpendicular band shows that there is an internal perturbation that arises from a $\Delta k = \pm 2$, $\Delta l = \pm 2$ coupling of the $l= 0$ and $l=\pm 2$ components. A level crossing is evident with the $l = 2$, $k = 11$ levels pushed to higher energy and the $l = 2$, $k = 14$ levels pushed to lower energy, for example. We have determined that the band center of the perturbing dark state is approximately $11 cm^{-1}$ below that of the bright state. The Hamiltonian including perturbing terms and fit constants will be presented. In addition, $\nu_{2}$, $\nu_{3}$, and $\nu_{4}$ have been measured and analyzed to reveal new details such as the splitting of the $K = 2$ and $K = 3$ levels.


(PNNL is operated for the US Department of Energy by the Battelle Memorial Institute under contract DE-AC06-76RLO 1830)
Author Institution: Pacific Northwest National Laboratory; Oregon State University; Department of Chemistry, Oregon State University; Department of Chemistry, National Science Foundation