Microwave spectroscopy of Lambda-doublet transitions in the ground state of CH

Abstract

The Lambda-doublet transitions in CH at 3.3 and 0.7 GHz are unusually sensitive to variations in the fine-structure constant and the electron-to-proton mass ratio. We describe methods used to measure the frequencies of these transitions with Hz-level accuracy. We produce a pulsed supersonic beam of cold CH by photodissociation of CHBr3, and we measure the microwave transition frequencies as the molecules propagate through a parallel-plate transmission line resonator. We use the molecules to map out the amplitude and phase of the standing wave field inside the transmission line. We investigate velocity-dependent frequency shifts, showing that they can be strongly suppressed through careful timing of the microwave pulses. We measure the Zeeman and Stark effects of the microwave transitions, and reduce systematic shifts due to magnetic and electric fields to below 1 Hz. We also investigate other sources of systematic uncertainty in the experiment.

arXiv comment27 pages, 12 figures

References in corpus (7)

• The fundamental constants and their variation: observational status and theoretical motivations
• Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant
• A search for varying fundamental constants using Hz-level frequency measurements of cold CH molecules
• $\Lambda$-doublet spectra of diatomic radicals and their dependence on fundamental constants
• Sensitivity of rotational transitions in CH and CD to a possible variation of fundamental constants
• Measurement of the lowest millimetre-wave transition frequency of the CH radical
• Pulsed beams as field probes for precision measurement

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