HgF excited-state spectroscopy enabling NSD-PV in 199Hg-based molecules

Nuclear-spin-dependent parity violation (NSD-PV) in molecules is enhanced in open-shell species with closely spaced opposite-parity levels, where electric-field tuning enables Stark-interference detection. A measurement is interpreted through molecule-specific electronic-structure parameters (e.g., WA) that map an observed PV matrix element onto hadronic weak couplings such as the nuclear anapole moment. We present our current HgF spectroscopy campaign aimed at the optical transitions required for state preparation and detection in a future NSD-PV experiment. Using laser spectroscopy and dispersed-fluorescence measurements on 199HgF, we assign low-lying excited-state manifolds and extract rovibronic and hyperfine constants and vibrational branching fractions relevant to quasi-closed photon cycling. These results provide a validated level map and cycling assessment for near-term HgF experiments and establish the molecular-structure inputs needed for NSD-PV interpretation in Hg-based diatomic and polyatomic molecular systems.