Hyperfine Structure and Isomeric Shift ofHg199m

The optical hyperfine structure and isotope shift in the 2537-Å line have been investigated. Two of the three components have been observed and measured. The magnetic-dipole-splitting factor $A\left({}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}\right)$ is -0.0771 ± 0.0005 ${\mathrm{cm}}^{-1\mathrm{}}$ and the isotope shift $\Delta S\left({}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}\right)$ is 0.112 ± 0.006 ${\mathrm{cm}}^{-1\mathrm{}}$ with respect to ${\mathrm{Hg}}^{198}$. The shift indicates staggering toward the heavier even isotope. An explanation is given in terms of nuclear deformation.