High accuracy measurements of methanol lines of astrophysical interest

The authors studied the accuracy of line frequency measurements up to sub kilohertz level of methanol lines used to probe possible proton-to-electron mass ratio variation. To determine the transition frequencies with high accuracy, series of pairs of full power and high sensitive frequency modulated channel records were performed. A new approach to high-precision Doppler limited resolution measurements of transition frequencies in millimeter wave range was proposed.