Methyl mercaptan (CH3SH) as a probe for $\mu$ variation

TL;DR

This paper calculates the sensitivity of methyl mercaptan's torsion-rotation transitions to variations in the proton-to-electron mass ratio, highlighting its potential as a probe for fundamental constant changes.

Contribution

It provides the first detailed sensitivity coefficients for methyl mercaptan, expanding the set of molecules used to test fundamental constant variations.

Findings

Sensitivity coefficients range from -14.8 to +12.2.

Transitions with excitation energy below 10 cm$^{-1}$ show notable sensitivity.

Methyl mercaptan is a promising candidate for probing $bc$ variation.

Abstract

Torsion-rotation transitions in molecules exhibiting hindered internal rotation possess enhanced sensitivities to a variation of the proton-to-electron mass ratio. This enhancement occurs due to a cancellation of energies associated with the torsional and rotational degrees of freedom of the molecule. This effect occurs generally in every internal rotor molecule, but is exceptionally large in methanol. In this paper we calculate the sensitivity coefficients of methyl mercaptan, the thiol analogue of methanol. The obtained sensitivity coefficients in this molecule range from $K_\mu=-14.8$ to $+12.2$ for transitions with a lower-level excitation energy below 10\,cm$^{-1}$.