Exciton Structure in the Ultraviolet Spectra of KI and RbI†*

Absolute reflectance data of KI and RbI were measured between 300° and 77°K in the range 4–11 eV. In both crystals, the first exciton is characterized by a peak reflectance of about 80% at 77°K followed by a strong antiresonance dip. Values of the dielectric parameters were obtained from a Kramers–Kronig analysis of the reflectance and are used to discuss the spectrum. The role of the line shapes and half-widths of the exciton peaks is emphasized in addition to spin–orbit interaction effects.