JOURNAL O F T H E A M E R I C A N CHEMICAL SOCIETY Regirlcrcd in
U.S. Pafcnl Ofice.
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VOLUME96, NUMBER 15
1974 by f h r American Chemical Socirly
JULY24, 1974
A Theoretical Study of Inner-Shell Photoionization Cross Sections and Angular Distributions Frank M. Chapman, Jr., and Lawrence L. Lohr, Jr.* Contributionf r o m the Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48104. Received August 28,1973 Abstract: Atomic photoionization cross sections and asymmetry parameters are calculated using a simple oneelectron model potential consisting of the positive nuclear charge at the origin surrounded by a series of negatively charged spherical shells. The radial Schrodinger equation is solved exactly for unbound states of the potential using Whittaker functions. Parameters for the model potential (shell radii and charges) are fitted using SCF charge densities. Applications are made to inner-shell ionizations of atoms and molecules as observed in ESCA (Mg K a and A1 K a photon energies), with emphasis on 1s ionizations for boron through neon and 2s and 2p ionizations for aluminum through argon. The periodic variation in cross section for ionization of a given orbital is discussed in terms of the photoelectron kinetic energy. Effects due to core relaxation are considered for the neon atom. The calculations are compared with experimental X-ray absorption coefficients and photoelectron spectral intensities.
P
hotoelectron spectroscopy using soft X-ray sources has recently become a widely used experimental technique for studying atoms, molecules, and solids. The basic experiment consists of bombarding a sample to be studied with nearly monoenergetic photons and measuring the properties of the ejected photoelectrons. Although most of the emphasis has centered around the energetics of the photoionization process leading to a determination of electron binding energies, with recent advances in the experimental technique it has become feasible to determine the intensity3 of photoelectron peaks as well as the angular (spatial) distribution4l5 of the ejected photoelectrons. With these additional parameters the experimentalist can begin to unravel more complex photoelectron spectra.6 The in( I ) (a) K. Siegbahn, C. Nordling, A. Fahlman, R. Nordberg, I
