SrF Rotational and Hyperfine Global Fit

Buoyed by the first polyatomic CaOH molecular trap, attention has shifted to heavier polyatomics like SrOH which provide an enhanced opportunity to observe parity non-conservation effects like the eEDM. Isoelectronic SrF was the first molecule successfully confined in a magneto-optical trap (MOT), and now SrF has also been slowed and trapped using Stark deceleration. Strontium has three stable, reasonably abundant isotopes: ⁸⁸Sr, ⁸⁷Sr, and ⁸⁶Sr. ⁸⁷Sr has a large I = ⁹/₂ nuclear spin and a sizeable nuclear electric quadrupole moment Q = +33 fm². Our global fit combines 6 data sets from 5 studies using laser/LIF-RF (Childs 1981, Azuma 1990) & laser-microwave (MW) (Domaille 1977, Ernst 1983) double-resonance and conventional MW (Schütze-Pahlmann 1982) techniques. This fit includes 114 measured transitions covering all 3 stable isotopologues with isotopic scaling and a BOB term for the electron spin-rotation γ. Vibrational and rotational states v = 0, 1, & 2 and N up to 75 are represented. The kHz precision of the RF data allows for significant improvement in both nuclear spin-rotation C_I terms and clarification of the Frosch-Foley c terms. This robust knowledge of SrF serves as a benchmark for both experimental and theoretical studies of SrF and more complex SrX(Y) molecules.