Hyperfine structure in the metastableDstates of atomic barium

The atomic-beam magnetic-resonance method has been used to measure the magnetic dipole and electric quadrupole hyperfine-structure interaction constants A and B for the ³D₃, ³D₂, and ¹D₂ states of the... $(6s)(5d)$ configuration for ¹³⁵Ba and ¹³⁷Ba. The experimental results for ¹³⁵Ba are A(¹D₂)=-73.429(4) MHz, B(¹D₂)=+38.710(15) MHz, A(³D₂)=+370.6(7) MHz, B(³D₂)=+18.3(22) MHz, A(³D₃)=+408.1(14) MHz, B(³D₃)=+20(8) MHz; and for ¹³⁷Ba, A(¹D₂)=-82.180(3) MHz, B(¹D₂)=+59.564(14) MHz, A(³D₂)=+413.9(9) MHz, B(³D₂)=+26.8(30) MHz, A(³D₃)=+455.4(16) MHz, B(³D₃)=+36(9) MHz. A comparison is made between the value of the electric quadrupole moment of the ¹³⁷Ba nucleus obtained from these results, which depend on the interaction of the $5d$ electron, and the value obtained from earlier results, which depend on the interaction of the $6p$ electron. There is a substantial difference in the values of Q(¹³⁷Ba) obtained from these two sets of measurements if one does not take the quadrupole shielding into account. Taking the quadrupole shielding into account markedly reduces this difference.