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The absorption structure of five light metals has been measured from the onset of Kand LII, 111-absorption up to photon energies of 140 eV (170 eV for Be). The edges a t the threshold are followed by several broad peaks which are distributed over the total energy region covered by these measurements. There is a striking similarity between the LII,III-absorption spectra of Na, Mg, and Al; a similarity can also be seen between the K-absorption spectra of Li and Be.Das optische Absorptionsverhalten yon fiinf Leichtmetallen wurde vom Einsatz der Kbzw. LII,III-Absorption bis zu Photonenenergieii von 140 eV (bei Be bis 170 eV) gemessen. Neben den Kanten beim Einsatz wurden im ganzen Spektralbereich mehrere breite Absorptionsmaxima beobachtet. Der allgemeine Verlauf der L~~,~~~-Absorptionsspektren von Na, Mg und A1 stimmt gut iiberein; Ahnlichkeiten zeigen sich auch bei den K-Absorptionsspektren von Li und Be.

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Recently interest in the absorption and emission structure near the onset of inner-shell transitions in simple metals has been revived in a series of theoretical papers. 1 " 9 Previously absorption at the edge was regarded as being due to transitions of core electrons into empty states just above the undisturbed Fermi level. This would explain a step in the absorption coefficient. The influence of the potential due to the deepstate hole was considered to be negligible because of immediate shielding by the conduction electrons. A more refined theoretical analysis yields the result that electron states in the vicinity of the Fermi surface are affected by the core potential in such a way that a singular behavior of the absorption and emission occurs at the edge 1 " 9 :where AE is the distance from the edge to higher (lower) energies in absorption (emission), \i is the absorption coefficient, respectively emission probability, a is expected to be positive for L nm transitions whereas it can also achieve negative values for K transitions. In the latter case a smoothing of the edge instead of a peak should be observed. We have considered Na as being an ideal metal to test these predictions because a peak near the onset could not be caused by a band singularity. Emission spectra of Na show a peak near the L um edge. 10 The only older absorption measurements which came to our attention are those of O'Bryan. 11 Though some peaking near the edge was observed we felt that a remeasurement with better techniques was desirable. s Synchrotron light from the Deutsches Elektronen-Synchrotron accelerator served as the source t.of radiation. The Na films were evaporated from nickel boats onto substrate films of Mg and Al which were surrounded by surfaces cooled to 77 °K. The base pressure in the system outside the cool trap was 10~6 Torr. The cooling served to i-lower water vapor pressure and has been proved * to be a good means 12 to get good metallic Na films without ultrahigh vacuum. The samples themselves were maintained at 77°K. Absorption was measured immediately after evaporation and it v was verified that none of the observed structures are caused by oxide. r Figure 1 shows our results. The absorption coefficient /i is given in arbitrary units since the n film thicknesses were not determined. The reproducibility of curves from different samples j-which were fitted at two points was within 3 % of 3 the total edge discontinuity. The accuracy of absolute energy calibration is ±0.05 eV.A peaking of the absorption towards the edge is 1 clearly recognized. The structure is somewhat 3 complicated by the spin-orbit splitting of the edge showing up as a separation of 0.17 ±0.02 eV. The observed intensity ratio of these two contribu-The absorption structure of sodium metals has been measured in the vicinity of the onset of 2p electron absorption. The results agree with theoretical investigations which claim a sharp absorption peak at the edge. 528

The absorption spectra of thin films of solid Ne and Ar have been measured in the photon energy range 25 to 500 eV. For comparison with the atomic states the corresponding spectra in the gas have also been investigated. The 7.5 GeV electron synchroton DESY served as light source. Near the onset of inner shell transitions (2 s in Ne, 3 s and 2 p in Ar) fine structure can be seen which is characteristic for the solid or atomic state. The structure in the spectra of the solid is ascribed to exciton and interband transitions. The absorption in the continuum at some distance from the various thresholds shows great similarities between the solid and gaseous states