It is shown that the exciton spectra in Pb${\mathrm{I}}_2$ can only be described in terms of a single Wannier series with a large ground-state anomaly. This anomaly is explained by a repulsive central-cell correction due to the cationic character of the exciton.

• Received 23 March 1972

DOI:https://doi.org/10.1103/PhysRevLett.28.1567