Atomic form factors and photoelectric absorption cross-sections near absorption edges in the soft X-ray region

Abstract

Reliable knowledge of the complex X‐ray form factor [Re(f) and Im(f)] and the photoelectric attenuation coefficient (σPE) is required for crystallography, medical diagnosis, radiation safety and XAFS studies. Key discrepancies in earlier theoretical work are due to the smoothing of edge structure, the use of non‐relativistic wave functions, and the lack of appropriate convergence of wave functions. These discrepancies lead to significant corrections for most comprehensive (i.e. all‐Z) tabulations. This work has led to a major comprehensive database tabulation [Chantler, C. T. (2000). J. Phys. Chem. Ref. Data, 29, 597–1048] which serves as a sequel and companion to earlier relativistic Dirac‐Fock computations [Chantler, C. T. (1995). J. Phys. Chem. Ref. Data, 24, 71–643]. The paper finds that earlier work needs improvement in the near‐edge region for soft X‐ray energies, and derives new theoretical results of substantially higher accuracy in near‐edge soft X‐ray regions. Fine grids near edges are tabulated demonstrating the current comparison with alternate theory and with available experimental data. The best experimental data and the observed experimental structure as a function of energy are strong indicators of the validity of the current approach. New developments in experimental measurement hold great promise in making critical comparisons with theory in the near future. This work forms the latest component of the FFAST NIST database [http://physics.nist.gov/PhysRefData/FFast02/Text/cover.html].