The Fine Structure of Certain X-Ray Absorption Edges

X-ray absorption edges for certain elements and compounds.---In a recent paper Coster¹ reports a white line on the long wave-length side of the x-ray absorption edge of some metallic oxides. Evidence is here reported which shows that in each case the white line is the absorption edge for some of the material which had been reduced to the metal by the x-ray beam. Screens were prepared by covering black paper with a thin layer of finely divided metal weighing 2 to 3 mg per cm². (1) K absorption edges for Ti(22), $V(23)$, Cr(24) and Mn(25) were found at 2489.5, 2261.9, 2064.9 and 1891.4 x-units. (2) LIII absorption edges for Sn(50), Sb(51) Te(52) and $I(53)$ are 3146.9, 2291.5, 2847.1 (Coster) and 2712 (Coster). These values are all in good agreement (within less than 1 x-unit) with the positions of Coster's white lines. (3) In the case of compounds of higher valence, the white line Coster obtained is therefore due to reduced element. (4) In the case of sulfides and sulfites, the secondary absorption edge at 4988 x-units reported by Lindh³ may likewise be due to traces of sulfate in the screen produced by the action of the x-rays.Chemical changes produced by x-rays.---Chemical evidence of appreciable reduction of iodic acid and of potassium permanganate is presented, and also of the oxidation of sulfurous acid.Theory of changes of valence produced by absorption of radiation by elements 22-25 and 50-53 and of consequent chemical changes.---It is proposed that the numerous electron transitions that follow the removal of an electron from its normal orbit by absorption of radiation may occasionally occur in such a way as to result in a change in the general electron configuration such that some of the valence electrons find stable positions farther in, thus resulting in a reduction of valence. Oxidation can also occur when the change in the electron configuration is such as to place an increased number of electrons in the valence group. What makes this proposal seem especially reasonable is that Ti(22), V(23), Cr(24) and Mn(25) occur in a portion of the periodic table in which inner groups are being filled in building new elements while Sn(50), Sb(51), Te(52) and I(53) are found very close to such a group. Bohr thus considers that configurations which place additional electrons in inner groups in this region are stable.