Part A. Theoretical Studies of the X-Ray Absorption Edge in Copper Complexes. Part B. Electron Correlation Consistent Calculation of Bond Dissociation Energies

Citation

Bair, Raymond Alan (1982) Part A. Theoretical Studies of the X-Ray Absorption Edge in Copper Complexes. Part B. Electron Correlation Consistent Calculation of Bond Dissociation Energies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ez8r-aj04. https://resolver.caltech.edu/CaltechTHESIS:03222018-144512817

Abstract

Part A: In order to elucidate the nature of the transitions involved in the x-ray absorption edge of molecular systems, we have used ab initio methods to examine the discrete transitions corresponding to the atomic 1s → 3d, 4s, 4p, 5s, and 5p transitions and the corresponding shakeup processes for Cu atom and for a Cu(II) model system, CuCl₂. The three common features of the K edge are described by the calculations. For CuCl₂, the lowest strong transitions have the character 1s → 4p (f = 0.00133). About 7.5 eV lower is a group of transitions involving 1s → 4p simultaneous with ligand-to-metal shakedown. About 18.7 eV below the main peak is a weak (65 times weaker) quadrupole-allowed transition corresponding to 1s → 3d (i.e., 1s₂3d₉ → 1s₁3d₁₀. In each case the spectral feature has been assigned to an allowed transition. Previously, the middle transition was assigned as 1s → 4s, whereas in this study the 1s → 4s transition was calculated to be too weak to be observed. We propose that the observed peak is due to the allowed transition involving 1s → 4p plus shakedown.

Part B: Ab initio generalized valence bond (GVB) and configuration interaction (CI) methods have been used to develop a generally applicable method for directly calculating bond energies. Particular effort has been put into obtaining a scheme in which all correlation terms that change upon dissociation of a particular bond are included consistently. The method uses in an essential way the localized orbitals from a GVB calculations, and is readily applicable to large systems [e.g., (CH₃)₃C-C(CH₃)₃]. To test our method, we selected two benchmark series of compounds, where the experimental bond energies are well known. Calculated bond energies are reported for the R-H bonds of CH₄, NH₃, H₂O, and HF, which are low by 3.5, 2.5, 3.0, and 2.7 .kcal/mol, respectively. We also report calculations of the R-R bond energies of C₂H₆, N₂H₄, H₂O₂, and F₂, which are low by 0.1, -3.2, -1.8, and 0.8 kcal/mol, respectively. In the application of our method, we have calculated all of the O-O, O-C, and O-H bond energies of HOOH, CH₃OOH, CH₃OOCH₃, CH₃OH, C₂H₅OH (O-H only), and CH₃O^-. Finally, we obtain the electron affinities of F, OH, and CH₃O with the same techniques.

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