Hyperfine structure in the metastable D states 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.