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 $\tilde{X} {}^2\Sigma^+ (010)$ state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the $\tilde{X} {}^2\Sigma^+ (010)$ 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 $\tilde{X} {}^2\Sigma^+ (010)$ ${}\rightarrow{}\tilde{A}{}^2\Pi_{1/2}(000)$ transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the $\tilde{X} {}^2\Sigma^+ (010)$ 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 $\tilde{X} {}^2\Sigma^+ (010)$ state and fit the molecule-frame dipole moment to $D_\mathrm{mol} = 2.16(1)$ 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 $\tilde{A}{}^2\Pi_{1/2}(000)$ state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.

Keywords

• polyatomic molecules
• precision measurement
• symmetry violation
• bending mode
• optical spectroscopy
• CP violation