Rotational spectroscopy of isotopic species of methyl mercaptan at millimeter and submillimeter wavelengths: CH₃³⁴SH^⋆,⋆⋆

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
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
⁵ Departments of Chemistry and Astronomy, The University of Virginia, Charlottesville, VA, USA
⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 29 March 2019
Accepted: 20 May 2019

Abstract

Methyl mercaptan (CH₃SH) is an important sulfur-bearing species in the interstellar medium, terrestrial environment, and potentially in planetary atmospheres. The aim of the present study is to provide accurate spectroscopic parameters for the most abundant minor isotopolog CH₃³⁴SH to support radio astronomical observations at millimeter and submillimeter wavelengths. The rotational spectrum of CH₃³⁴SH, which is complicated by the large-amplitude internal rotation of the CH₃ group versus the ³⁴SH frame, was investigated in the 49−510 GHz and 1.1−1.5 THz frequency ranges in natural isotopic abundance. The analysis of the spectrum was performed up to the second excited torsional state, and the obtained data were modeled with the RAM36 program. A fit within experimental accuracy was obtained with a RAM Hamiltonian model that uses 72 parameters. Predictions based on this fit are used to search for CH₃³⁴SH with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the hot molecular core Sgr B2(N2), but blends with emission lines of other species prevent its firm identification in this source.