Spectroscopic characterization of buffer-gas-cooled lead monofluoride molecules in the B2Σ+(υ’ = 0) ← X12Π1/2(υ = 0) transition

Abstract

Establishing a nonzero measurement of the electron Electric Dipole Moment (eEDM) has long been a fundamental pursuit in atomic, molecular and optical physics, offering possible insights into new physics beyond the Standard Model. In this regard, lead monofluoride (PbF) has emerged as a potential candidate for measuring eEDM primarily due to its suitable properties such as the strong internal effective electric field, and eEDM-sensitive ground state with large Ω-doubling and small magnetic g factor. In this article, we realize the production of a buffer-gas-cooled PbF molecular beam and characterize its high-resolution spectroscopy in the B2Σ+(υ’=0) ← X12Π1/2(υ = 0) transition, including both direct absorption and laser-induced fluorescence spectroscopy. A highly concentrated beam of PbF molecules is obtained at its central forward velocity of 223 ± 17 m/s, while 81, 66 and 24 hyperfine-resolved spectral lines with an accuracy of 40 MHz have been assigned respectively for 208PbF, 207PbF and 206PbF isotopologues. The hyperfine constants due to the 19F nucleus (A\\parallel and A⊥) of the B state are reported for the first time, and those of the 207Pb nucleus have been also updated. Such a cryogenic molecular beam of PbF in association with its hyperfine-resolved spectral atlas of B2Σ+(υ’=0) ← X12Π1/2(υ = 0) will be essential in developing sensitive detection schemes towards the eEDM measurement.