The Dependence of X-ray Absorption Spectra upon Chemical and Physical State

The x-ray absorption spectra of As, Se, Br, Zn, Hg, Xe, and Kr, and of compounds of some of these elements have been photographed for both the solid and the vapor states at a dispersion of about 5 X.U. per mm. The effect of the chemical and physical state of the absorbing atom upon the secondary structure which lies to the short wave-length side of the main absorption edge was investigated. It was found that: (1). The monatomic vapors Zn, Hg, Xe, and Kr exhibit no secondary structure at distance from the main edge greater than the ionization potential of the atom. (2). Polyatomic vapors usually, though not necessarily, have a secondary structure similar to that which is exhibited by the same molecule in the solid state. (3). For a polyatomic molecule in the solid state there is often an additional structure observed which is absent when the molecule is in the vapor state. (4). There is an additional structure in the secondary absorption of solid NaBr${\mathrm{O}}_3$ which is not observed in a solution of NaBr${\mathrm{O}}_3$. (5). Completed electron shells of atoms in the solid state do not necessarily mean the absence of secondary absorption edges as has been suggested. In order to account for this dependence of secondary absorption on molecular and physical state it is suggested that perhaps the secondary discontinuities correspond to the excitation energies of the structure electrons postulated by O. W. Richardson.