Hyperfine Structure and Electric Dipole Moment of BaF X²Σ+

Molecular‐beam laser‐microwave double‐resonance spectroscopy was applied to study rotational transitions in the X 2Σ+, v=0 state of BaF at high resolution. From the analysis of the fluorine hyperfine structure (hfs) the magnetic hfs parameters were determined as b=63.509 (32) MHz and c=8.224 (58) MHz (statistical standard deviation in parentheses). Additional Stark effect measurements yielded and electric dipole moment μ=3.170(3) D. The magnetic hfs is interpreted as an effect of fluorine electron spin polarization. Mixing coefficients for Ba+ hybridization are estimated and compared with the charge distribution derived from the measured dipole moment in terms of an ionic bonding model.