Rotational spectroscopy of methyl mercaptan CH₃³²SH at millimeter and submillimeter wavelengths^⋆,⋆⋆

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: zakharenko@ph1.uni-koeln.de, hspm@ph1.uni-koeln.de
² Institute of Radio Astronomy of NASU, Mystetstv 4, 61002 Kharkiv, Ukraine
e-mail: ilyushin@rian.kharkov.ua
³ Quantum Radiophysics Department, V. N. Karazin Kharkiv National University, Svobody Square 4, 61022 Kharkiv, Ukraine
⁴ Department of Physics, University of New Brunswick, Saint John, NB, Canada

Received: 24 April 2019
Accepted: 25 July 2019

Abstract

We present a new global study of the millimeter (mm) wave, submillimeter (sub-mm) wave, and terahertz (THz) spectra of the lowest three torsional states of methyl mercaptan (CH₃SH). New measurements have been carried out between 50 and 510 GHz using the Kharkiv mm wave and the Cologne sub-mm 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 K_a up to 18, were combined with previously published measurements and fit 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 (MW) and 16 345 far-infrared line frequencies sampling transitions within and between the ground, first, and second excited torsional states. This investigation presents a two-fold expansion in the J quantum numbers and a significant improvement in the fit quality, especially for the MW part of the data, thus allowing us to provide more reliable predictions to support astronomical observations.