O n the X-Ray absorption fine structures with polarised X-Rays K r o g s t a d , N e l s o n and S t e p h e n s o n l ) while testing q u a n t i t a t i v e l y Kronig's idea regarding the sharpness of the X -r a y absorption fine-structures to be obtained by using single slab crystals as absorbers and polarised X-rays as the incident radiation, discovered in addition a v e r y peculiar phenomenon --the shift in the position of the structures on changing the orientation of the crystal. The object of this note is to suggest a possible explanation for such a shift. Their experiment was carried out with a double crystal spectrometer, in which the first reflecting crystal was of calcite and acted as a polariser. The second crystal was used simultaneously as the absorber and reflector. NaC1 and KC1 were chosen for the purpose and the chlorine Kedge was studied in both. The plane of reflection in both was kept as (100). When the orientation of the NaCl-crystal was so altered that the direction of ejection of the photo-electrons was changed from being perpendicular first to (110) and then to (100) planes, the beta peak of the structures was found to shift by 3.7 eV. No such effect was found for KC1. The alpha peak was not shifted, while peaks beyond beta are not reported in the data for NaCI.
I t is quite obvious t h a t NaC1 and KC1 have exactly similar structures, only differing in their lattice parameter. Therefore any shift due to structural changes might be excluded. The beta-peak shift clearly indicates a shift in the energy level of the solid state. E q u a t i o n to the level is 3