Optical Absorption of Solid Krypton and Xenon in the Far Ultraviolet

Photoabsorption caused by transitions of the $3d$ electrons in solid Kr and of the $4d$ and $4p$ electrons in solid Xe has been measured. The 7.5-GeV electron synchrotron DESY served as a light source. As a comparison, the corresponding transitions in the gas have been remeasured. At the onset of $d$-electron transitions, in both solid Kr and solid Xe, absorption-line series have been found, which have been identified as "forbidden" excitons in terms of Elliot's theory. At some distance from the onset, the broad maximum found earlier in gas absorption and ascribed to the delayed onset of $d\to f$ transitions can also be seen in the solids.