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Prospects for high-resolution microwave spectroscopy of methanol in a Stark-deflected molecular beam

Recently, the extremely sensitive torsion–rotation transitions in methanol have been used to set a tight constraint on a possible variation of the proton-to-electron mass ratio over cosmological time scales. In order to improve this constraint, laboratory data of increased accuracy will be required. Here, we explore the possibility for performing high-resolution spectroscopy on methanol in a Stark-deflected molecular beam. We have calculated the Stark shift of the lower rotational levels in the ground torsion-vibrational state of CH3OH and CD3OH molecules, and have used this to simulate trajectories through a typical molecular beam resonance set-up. Furthermore, we have determined the efficiency of non-resonant multi-photon ionisation of methanol molecules using a femtosecond laser pulse. The described set-up is in principle suited to measure microwave transitions in CH3OH at an accuracy below 10−8.