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 Title: Very High Frequency EPR: Instrument and Applications Author(s): Wang, Wei Doctoral Committee Chair(s): Belford, R. Linn Department / Program: Chemistry Discipline: Chemistry Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Physical Physics, Molecular Abstract: Most Electron Paramagnetic Resonance (EPR, also known as ESR or EMR) experiments are performed at conventional 9 GHz or 35 GHz frequency. But there are numerous situations in which a large increase in the microwave frequency (and/or magnetic field) will result in substantial increase in the information content in EPR spectra. This has motivated us to construct a very high frequency (VHF, 95 GHz) EPR spectrometer at Illinois EPR Research Center. Many advantages of VHF EPR are demonstrated through examples in Chapter 1. The spectrometer and some unique aspects of the instrument are described and documented in Chapter 2. Chapter 3 reports use of the VHF EPR technique to study the structure/spectral relationship of a homologous series of thiophenes, which may be constituents of coal. Two successful methods to generate the cation radicals of these organic sulfur compounds are found. The g matrices (tensors) of the thiophenic radicals are obtained for the first time. The small differences between anisotropic components of the g matrices can be unambiguously resolved. Correlations of the experimentally measured g matrices with the molecular and electronic structures are reported. The g shifts correlate linearly with $\lambda$ of their Huckel molecular orbitals; the largest g components are proportional to the $\pi$ spin densities on sulfur. In addition, the small proton hyperfine interactions of dibenzothiophene (DBT) are observed for the first time by continuous wave VHF EPR. A multifrequency approach, including auxiliary 2-4 GHz pulsed measurement, has shown that a single set of spin Hamiltonian parameters describes the spin system of DBT over a microwave frequency span of 3 to 95 GHz. These newly available, detailed, and accurate data provide a valuable opportunity to test, and perhaps to improve, the existing theoretical models for predictions on g matrices of organic radicals. Finally, Chapter 4 reports trial calculations of g matrices by several molecular orbital methods. Issue Date: 1993 Type: Text Description: 234 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993. URI: http://hdl.handle.net/2142/72286 Other Identifier(s): (UMI)AAI9329194 Date Available in IDEALS: 2014-12-17 Date Deposited: 1993
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