# FITTING AND PREDICTING INTERNAL ROTOR SPECTRA USING FOURIER EXPANSIONS OF THE MOLECULAR PARAMETERS - APPLICATION TO THE $HCl0_{4}$ TORSION ROTATION SPECTRUM

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 Title: FITTING AND PREDICTING INTERNAL ROTOR SPECTRA USING FOURIER EXPANSIONS OF THE MOLECULAR PARAMETERS - APPLICATION TO THE $HCl0_{4}$ TORSION ROTATION SPECTRUM Creators: Oh, J. J.; Cohen, E. A.; Pickett, H. M. Issue Date: 1993 Publisher: Ohio State University Abstract: The general asymmetric rotor programs by Pickett have been modified to allow expansion of the molecular parameters as Fourier series in $\rho K/3$. The method takes advantage of the fact that the expectation values of the operators in the Mathieu equation may be expanded in such a way, but avoids the problems of making a particular selection of torsion-rotation interaction terms. Several molecules with methyl groups and three-fold barriers have been fit to within experimental error in this manner for the purpose of cataloging their spectra. Perchloric acid, $HClO_{4}$, which has a heavy internal top, moderately low barrier $(s \approx 5.15)$, and several avoided crossings in the torsional ground state will be used as an illustration of the application of the program. Approximately 400 features covering the range $0 < J < 50,0 < K < 40$ have been well fitted. The $HClO_{4}$ spectrum will be reviewed and the derived parameters will be discussed. Description: Author Institution: Jet Propulsion Laboratory, California Institute of Technology URI: http://hdl.handle.net/1811/18668 Other Identifiers: 1993-TH-10