Torsion-Rotational Transitions in Methanol as a Probe of Fundamental Physical Constants—Electron and Proton Masses

We report on the using of torsion-rotational transitions in the CH₃OH and ¹³CH₃OH molecules to evaluate possible variations of the electron-to-proton mass ratio μ = m_e/m_p from spectral observations of emission lines detected in the microwave range towards the dense molecular cloud Orion-KL. An estimate of the upper limit on the relative changes in μ is obtained by two independent ways with ¹³CH₃OH lines and with the combination of ¹³CH₃OH and CH₃OH lines. The calculated upper limit Δμ/μ < 1.1 × 10^–8(1σ) is in line with the most stringent constraints on the variability of fundamental physical constants established by other astrophysical methods.