Quadrupole Moments ofAs75,La139,andHg201

Abstract

It is shown that the level $5d^{3}4s{}_{}{}^5{}_{}{}^{}F_1^{}{}_{}{}^{}$ of Ta ii is approximately free from perturbation, making the calculation of the quadrupole moment simple. Then it is shown that the quadrupole coupling constant (measured by Brown and Tomboulian) in the hyperfine structure (hfs) of this level can be interpreted if one assumes a rather large antishielding effect $\Delta \left(5\mathrm{}{d}^{3}4s\right)=-0.77$. In the course of the calculation the magnetic moment $\mu \left({\mathrm{Ta}}^{181}\right)=2.4\mathrm{}\pm 0.2$ nm was obtained. Upon assuming the shielding corrections $\Delta \mathrm{}\left(5d6s\right)=-0.3\mathrm{}$ and $\Delta \mathrm{}\left(6s6p\right)=-0.1\mathrm{}$ for any heavy element around Lu, the quadrupole moments $Q\left({\mathrm{La}}^{139}\right)={0.2}_1\pm 0.04$ barn and $Q\left({\mathrm{Hg}}^{201}\right)={0.4}_2\pm 0.04$ barn were obtained. In the case of La ii $5d4f{}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{}$, a negative (instead of positive) quadrupole moment was obtained by neglecting the shielding correction. This can be interpreted by assuming a large antishielding effect in the $4f$ electron. In connection with this a tentative value $Q\left({\mathrm{Er}}^{167}\right)=4\mathrm{}$ barns was deduced. Upon assuming $\Delta \mathrm{}\left(4p5s\right)=-0.16\mathrm{}$ for the hfs of the spectrum of As ii, the value $Q\left({\mathrm{As}}^{75}\right)=0.27\mathrm{}\pm 0.04$ barn was obtained. From the hfs of a level of the configuration $4p5p$ of As ii, the value 0.12±0.07 barn was obtained, the shielding correction being neglected; and this is interpreted to be due to a possible large antishielding effect in the $5p$ electron. The same tendency seems to be detectable in the published determination of $Q\left({\mathrm{K}}^{39}\right)$ from the $5p$ state of K i.