INFRARED COMBINATION BANDS AND VIBRATIONAL ANHARMONICITY IN SULFUR HEXAFLUORIDE
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Date
1982
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Publisher
Ohio State University
Abstract
An extended investigation of the infrared spectrum of combination, overtone, and difference bands of gaseous $SF_{6}$ has been undertaken to elucidate the anharmonicity constants and hence the nature of excited vibrational states. Spectra were obtained on an FTIR spectrometer at a resolution of $0.04 cm^{-1}$. Some 15 combination and difference bands of $^{31}SF_{6}$ have analyzed by fitting a polynomial expression to P-and R-branch manifold frequencies. These analyses yield the scalar spectroscopic constants together with values for $B\zeta, \zeta$, and the centrifugal distortion constant D. Some of these bands $(\upsilon_{2}+\upsilon_{4}, for example)$ exhibit more than one progression in each branch duo to the presence of $P^-$ and $R^{+}$ transitions together with the usual $P^{+}$ and $R^{-}$; these can be separately assigned and the effective Coriolis constants $\zeta$ determined. In addition to these bands, there are about 15 more that can not be analyzed at FTIR resolution, but which have sharp Q-branch edges from which the band origins can be estimated. All of these data have been combined to yield precise values for the 21 anharmonicity constants $X_{iji}$ most of these have been determined with accuracies of the order of $0.01 to 0.003 cm^{-1}$. The higher vibrational levels of $SF_{6}$ will be discussed.