Spectroscopic studies of alkali and zinc core levels in alkali metals

The results of a systematic investigation of the core excitation spectra of alkali and Zn impurities in alkali metal hosts are described. The excitation channels involved are the np6(n+l)s ~ np5(n+l)s2 transitions of 10 2 9 2 Cs(n=5), Rb(n=4) and K(n=3) cores, and the 3d 4s ~ 3d 4s 4p transitions of the Zn 3d core. The data were obtained by differential reflectance spectroscopy using synchrotron radiation on alloys quench-condensed at liquid He temeratures. Various excitation profiles at threshold are observed for alkali core excitations in alkali-alkali alloys. These profiles change systematically among the alloys, and apparently belong to a universal sequence of line2 shapes. By choice of alkali host, some (n+l)s levels can be made to lie below or in the conduction band, and this influences the lineshape. The lineshape for any particular alloy can be predicted from a dimensionless parameter ~ which is the ratio of perturbing potential to conduction band kinetic energy in the excited configuration. The famous X-ray edge anomaly, a sharp spike at threshold observed in some pure metals, occurs only in the limit of the sequence when ~ is large. Two distinct types of core excitation profiles are observed for Zn in alkali metal hosts. The transition between them again coincides with the transition of the excited orbital from in the band to below it. The profile exhibits a strong interference with a background of conduction band excitations. This allows the lifetime against decay of the local configuration into the electron-hole pair continuum to be determined. The lifetime iv \ is insensitive to the particular alkali host lattice and to the location of the Zn center on the surface or in the bulk. Instead, the striking change of lineshape takes place because the distribution of oscillator strength is changed when the 4p level mixes into the conduction band.U of I OnlyThesi