Field-free, Stark, and Zeeman spectroscopy of the Ã2Π1/2−X̃2Σ+ transition of ytterbium monohydroxide

The $0_0^0\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$, $1_1^0\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$, and $1_0^1\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$ bands of an internally cold molecular beam sample of ytterbium monohydroxide, YbOH, have been recorded at the near natural linewidth limit and analyzed to determine the fine structure parameters. Numerous lines in the $0_0^0\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$ band associated with the lowest rotational levels were recorded in the presence of a static electric field and analyzed to determine the magnitude of the molecular frame permanent electric dipole moment, $|{\vec{\mu }}_{el}|$, for the $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(0,0,0)$ and $\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(0,0,0)$ states of 1.9(2) and 0.43(10) D, respectively. An electrostatic polarizability model is used to predict the ${\vec{\mu }}_{el}$ for the $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(0,0,0)$ state. The $0_0^0\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$ band is recorded in the presence of a weak static magnetic field to observe the electric dipole allowed transitions having $\mathrm{\Delta }J=-2$, which are used to assist in the rotational quantum number assignment and confirm the identity of the excited state. An expression for the $\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(0,0,0)$ magnetic $g$ factor is derived and shown to correctly model the observed magnetic tuning. A comparison with YbF is made and implications for the use of YbOH as a venue for symmetry violation measurements are discussed.