Calculation of Copper K-Edge Photoabsorption Spectra Using AN Extended Continuum Multiple Scattered Wave Method.

X-ray absorption spectra are characterized by a sharp increase, or 'edge', in the absorption cross section at an energy corresponding to the ionization energy of the photoelectron. Superposed on a smooth rising edge is structure which is characteristic of the electronic structure and molecular geometry about the photoabsorbing atom. The features can most generally be attributed to transitions to bound final states of the photoelectron and resonances in continuum final states. In this work we have used a Multiple Scattered Wave-X(alpha) Extended Continuum method (MSW-X(alpha)-EC) for studying the complete near-edge structure both below and above the ionization threshold. This one-electron theory is based on a muffin-tin approximation to the molecular potential. The extended continuum method permits the treatment of the bound final states of the photoelectron with continuum boundary conditions. In doing so, a much more expedient calculation of the near-edge structure is made possible, since the construction of a self-consistent potential is no longer necessary. Several molecular systems are investigated using the MSW-X(alpha)-EC method. The polarized K-edges of several square-planar copper(II) molecules are computed, including single-ligand and mixed-ligand systems. In addition, the K-edges of several copper(I) complexes were considered. We have found the one-electron MSW-X(alpha)-EC method successful in accounting for all primary spectral features in the near-edge. A brief review of previous and current efforts to explain the x-ray absorption spectra is given in Chapter I. In Chapter II the details of the MSW-X(alpha)-EC method are discussed and Chapter III presents a test of the extended continuum method on a simple molybdenum complex. The K -edges of the tetrahedrally coordinated complex bis(2,5 -dithiahexane)copper(I) and the square planar complex creatininium tetrachlorocuprate(II) are discussed in Chapters IV and V respectively. In Chapter VI two square planar and one flattened tetrahedral trans-mixed ligand copper(II) complexes are investigated. In Chapter VII the polarized copper K-edge of the single ligand square planar complex tetrakis(1,4,5 -trimethylimidazole)copper(II) diperchlorate is studied and in Chapter VIII the linear copper(I) system copper(1,3,5 -trimethylpyrazole)(,2)BF(,4) is considered. Given in Chapter IX is a summary and discussion of the MSW-X(alpha)-EC method and the results of the copper(II) and copper(I) systems studied.