Interpretation of the Isomeric Chemical Shifts inAu197

The large chemical shifts recently observed in Mössbauer absorption experiments on ${\mathrm{Au}}^{197}$ are explained on the basis of Coulombic interaction between the $6s$ electron of gold and the $3s_{\frac{1}{2}}$ and $2d_{\frac{3}{2}}$ protons. A first-order perturbation calculation is made, using the Coulombic potential within the nucleus due to the $6s$ electron. Proton wave functions derived from harmonic-oscillator, square-well, and Woods-Saxon nuclear potentials are treated. The latter two potentials yield results that are in reasonable accord with experiment. This model can afford a sensitive comparison of nuclear potentials as well as a determination of the $s$ conduction-electron density on impurity atoms. In particular, this calculation discriminates against the harmonic-oscillator potential and shows that the $6s$ electron density on a gold impurity atom in several hosts is higher than in pure gold. These results also indicate that the $3s_{\frac{1}{2}}$ proton subshell is filled in the ground state of ${\mathrm{Au}}^{197}$.