Fine and hyperfine interactions in 171YbOH and 173YbOH.

The odd isotopologues of ytterbium monohydroxide, 171,173YbOH, have been identified as promising molecules to measure parity (P) and time reversal (T) violating physics. Here, we characterize the A2Π1/2(0,0,0)−X2Σ+(0,0,0) band near 577 nm for these odd isotopologues. Both laser-induced fluorescence excitation spectra of a supersonic molecular beam sample and absorption spectra of a cryogenic buffer-gas cooled sample were recorded. In addition, a novel spectroscopic technique based on laser-enhanced chemical reactions is demonstrated and used in absorption measurements. This technique is especially powerful for disentangling congested spectra. An effective Hamiltonian model is used to extract the fine and hyperfine parameters for the A2Π1/2(0,0,0) and X2Σ+(0,0,0) states. A comparison of the determined X2Σ+(0,0,0) hyperfine parameters with recently predicted values [Denis et al., J. Chem. Phys. 152, 084303 (2020); K. Gaul and R. Berger, Phys. Rev. A 101, 012508 (2020); and Liu et al., J. Chem. Phys. 154,064110 (2021)] is made. The measured hyperfine parameters provide experimental confirmation of the computational methods used to compute the P,T-violating coupling constants Wd and WM, which correlate P,T-violating physics to P,T-violating energy shifts in the molecule. The dependence of the fine and hyperfine parameters of the A2Π1/2(0,0,0) and X2Σ+(0,0,0) states for all isotopologues of YbOH are discussed, and a comparison to isoelectronic YbF is made.