Characterizing the fundamental bending vibration of a linear polyatomic molecule for symmetry violation searches

Abstract

Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic X ˜ 2 Σ + ( 010 ) state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the X ˜ 2 Σ + ( 010 ) state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of 174 YbOH using high-resolution optical spectroscopy on the nominally forbidden X ˜ 2 Σ + ( 010 ) → A ˜ 2 Π 1 / 2 ( 000 ) transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the X ˜ 2 Σ + ( 010 ) state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the X ˜ 2 Σ + ( 010 ) state and fit the molecule-frame dipole moment to D m o l = 2.16 ( 1 ) D and the effective electron g-factor to g S = 2.07 ( 2 ) . Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin-orbit and vibronic perturbations in the excited A ˜ 2 Π 1 / 2 ( 000 ) state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.