Hyperfine Structure ofHg197andHg199

The hyperfine structure of the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of ${\mathrm{Hg}}^{197}$ and ${\mathrm{Hg}}^{199}$ has been measured by a microwave-optical experiment. This involves optical excitation to the desired state, paramagnetic resonance in this state, and an optical method of detecting the paramagnetic resonance. The paramagnetic resonances were obtained between different $F$ levels as a function of magnetic field. Quadratic Zeeman corrections were estimated by second-order perturbation theory and the corrected transition frequencies were then extrapolated to zero field. The zero-field hyperfine-structure splittings in the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state are ${\mathrm{Hg}}^{197}(F=\frac{3}{2} \mathrm{to} F=\frac{1}{2})=23\mathrm{}086.37\left(2\right)\mathrm{}$ Mc/sec, ${\mathrm{Hg}}^{199}(F=\frac{3}{2} \mathrm{to} F=\frac{1}{2})=22\mathrm{}128.56\left(2\right)\mathrm{}$ Mc/sec. Hyperfine-structure constants $A$ are obtained which are correct to second order. These are combined with the known nuclear magnetic moments to give the hyperfine-structure anomaly in the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state: $\Delta ({}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}, {\mathrm{Hg}}^{199}, {\mathrm{Hg}}^{201})=-0.00147\mathrm{}\left(1\right)\mathrm{}$, and the anomaly of the hyperfine-structure interaction for the $6s$ electron in the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state: $\Delta (s_{\frac{1}{2}}, {\mathrm{Hg}}^{199}, {\mathrm{Hg}}^{201})=-0.00175\mathrm{}\left(9\right)\mathrm{}$.