The Nuclear Moment of Barium as Determined from the Hyperfine Structure of the Ba II Lines

The hyperfine structure of the Ba II lines $\lambda 4934\mathrm{A}$ and $\lambda 4554\mathrm{A}$ has been observed. The relative intensities of the observed components of $\lambda 4554\mathrm{A}$ have been measured. From these data it was possible to determine the value of the nuclear moment of ${\mathrm{Ba}}^{135,137}$, if it is assumed that the barium isotopes 136 and 138 have no nuclear spin. The most probable value obtained for $i$ is $\frac{5}{2}$. The separation of the hyperfine levels of $6s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ is 0.272 ${\mathrm{cm}}^{-1\mathrm{}}$, of $6p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ is 0.039 ${\mathrm{cm}}^{-1\mathrm{}}$, and of $6p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ is approximately 0.033 ${\mathrm{cm}}^{-1\mathrm{}}$. In all other terms the hyperfine splitting is very small. There is some evidence that there is an isotopic shift of the center of gravity of the levels of the odd isotopes with respect to the even isotopes, and it has a probable value of 0.022 ${\mathrm{cm}}^{-1\mathrm{}}$ for the ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ state, and 0.017 ${\mathrm{cm}}^{-1\mathrm{}}$ for the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state.