Rotational spectroscopy of methyl mercaptan CH$_3$$^{32}$SH at millimeter and submillimeter wavelengths

TL;DR

This study provides an extensive analysis of methyl mercaptan's millimeter, submillimeter, and terahertz spectra, improving spectral models and predictions to aid astronomical detection and analysis.

Contribution

It offers a comprehensive, high-precision spectral dataset and an improved torsion-rotation Hamiltonian model for methyl mercaptan, expanding quantum number coverage and accuracy.

Findings

Expanded spectral data up to J=61 and Ka=18.

Achieved a root-mean-square deviation of 0.72 for the fit.

Enhanced spectral predictions for astronomical observations.

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 (CH$_3$SH). 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 16345 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.