The isotopic shift of the 6${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$→6${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ (1.28 μm) magnetic-dipole transition in Pb, which had been previously estimated incorrectly in the literature, has been measured, together with the magnetic hyperfine constant of the ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ level in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$. The shifts of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ lines from the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ position are δ(206–208)=220.4(15) MHz and δ(207–208)=138.0(17) MHz, and the hyperfine constant A(6${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$)=-2388.2(45) MHz. Inclusion of the shifts in calculated optical rotation line shapes removes long-standing discrepancies between theory and experiment, which have limited the precision of parity-nonconservation measurements in Pb.

• Received 8 April 1991

DOI:https://doi.org/10.1103/PhysRevA.44.R1439