Field-free, Stark, and Zeeman spectroscopy of the $\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$ 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.

Figure 1

The laser excitation spectrum in the region of the $0_0^0\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$ band head of YbOH. The assignment and stick spectra associated with the ${}^{174}\mathrm{YbOH}$ and ${}^{172}\mathrm{YbOH}$ isotopologues were obtained using a rotational temperature of 20 K and the optimized parameters.

Figure 2

The laser excitation spectrum in the region of the $1_1^0\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$ band of YbOH. The assignment and stick spectrum associated with the ${}^{174}\mathrm{YbOH}$ isotopologue were obtained using a rotation temperature of 20 K and the optimized parameters.

Figure 3

The observed laser excitation spectrum in the region of the $1_0^1\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}-\tilde{X}{}^2{\mathrm{\Sigma }}^{+}$ band head of YbOH. The assignment and stick spectrum associated with the ${}^{174}\mathrm{YbOH}$ isotopologue were obtained using a rotation temperature of 20 K and the optimized parameters. The unusual ordering of the branches is caused by the unusually large Λ doubling in the $\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(1,0,0)$ state.

Figure 4

Left: The field-free and Stark spectra for the ${}^{R}R_{11}$(0) line with parallel polarization ($\mathrm{\Delta }{M}_J=0$) and a field strength of 3038 V/cm. Right: The associated energy levels for the ${}^{174}\mathrm{YbOH}$ isotopologue as a function of electric field strength and assignment.

Figure 5

Left: The field-free and optical Zeeman spectra in the vicinity of the ${}^{O}P_{12}$(3) line recorded at a field of 64 G with parallel polarization ($\mathrm{\Delta }{M}_J=0$). The predicted spectrum for the ${}^{174}\mathrm{YbOH}$ isotopologues was obtained using a narrower linewidth than that of the observed spectrum (10 MHz vs 30 MHz) to highlight the underlying splitting. Right: The energy level tuning for the ${}^{174}\mathrm{YbOH}$ isotopologue as function of magnetic field strength along with the assignment. The effecting $g_J$-factor for the ground and excited state levels of the induced ${}^{O}O_{11}$(3) line are of the same magnitude and sign resulting in a sharp spectral feature whereas those for the ${}^{O}P_{12}$(3) line are of the same magnitude but opposite sign resulting in a broad, partially resolved, spectral feature. The spacing between the ${}^{O}O_{11}$(3) induced transition and ${}^{O}P_{12}$(3) line provides a direct measure of the ρ doubling in the $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(0,0,0)$ state.