Using laser-induced nuclear-orientation and optical-saturation techniques, we have produced sub-Doppler changes in the anisotropy of the angular distribution of the 514-keV γ rays from the 1-μs isomer ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}_{}^{\mathit{m}}{}_{}{}^{}$. This permits high-resolution measurements of D1 and D2 hyperfine transitions of atoms of the isomer, which give the isomer’s nuclear electric quadrupole moment, -0.73±0.17 b, and its nuclear magnetic dipole moment, (6.043±0.005)${\mathrm{\mu }}_{\mathit{N}}$. The isomer shift, -113±8 MHz relative to the ground state of ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$, corresponds to a change in the mean-square charge radius of +0.174±0.008 ${\mathrm{fm}}^2$.

• Received 30 October 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.1681