Global Fits for AlCl, BiCl, and BiF: Benchmarks for Novel Physics

New global fits combining existing rotational spectroscopy data for the Cl isotopologues of both AlCl (e.g. Hensel, et al. 1993 & Hoeft, et al. 1973) and BiCl (Kuijpers, et al. 1976) provide much improved precision in important molecular parameters for their use in novel physics applications, including hyperfine and Born-Oppenheimer Breakdown (BOB) terms. Another new fit combining data for a range of several rotational transitions in a number of vibrational states achieves similar results for BiF (Kuijpers & Dymanus 1977), providing another benchmark molecule for theoretical work on molecules used in eEDM and related searches. For example, uncertainties in the bismuth nuclear electric quadrupole eQq hyperfine values for BiF and BiCl are reduced by a factor of 3 and 8, respectively. The resulting precise ratios of the nuclear electric quadrupole moments Q(³⁷Cl):Q(³⁵Cl) for disparate AlCl and BiCl are quite consistent with each other as well as with further atomic and molecular spectroscopic measurements. This information bears directly on the oft-complicated nuclear physics reference work Q-value choices for both Cl isotopes.