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Description
We present a new global study of the millimeter wave, submillimeter wave, and THz spectra of the lowest three torsional states of methyl mercaptan (CH_3_SH). New measurements have been carried out between 50 and 510GHz using the Kharkiv mm wave and the Cologne submm wave spectrometers whereas THz spectra records were used from our previous study. The new data involving torsion-rotation transitions with J up to 61 and Ka up to 18 were combined with previously published measurements and fitted using the rho-axis-method torsion-rotation Hamiltonian. The final fit used 124 parameters to give an overall weighted root- mean-square deviation of 0.72 for the dataset consisting of 6965 microwave and 16345 FIR line frequencies sampling transitions within and between the ground, first, and second excited torsional states of the molecule. This investigation presents a twofold expansion in the J quantum numbers and a significant improvement in the fit quality, especially for the microwave part of the data thus allowing us to provide improved predictions to support astronomical observations.
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