Very high frequency EPR: Instrument and applications. [EPR (electron paramagnetic resonance)]

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7267686

Wang, Wei

Most Electron Paramagnetic Resonance (EPR) experiments are performed at conventional 9 GHz or 35 GHz frequency. 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 the author 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 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 Heuckel 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 auxilliary 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.

• Research Organization: Illinois Univ., Urbana, IL (United States)
• OSTI ID: 7267686
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102* -- Chemical & Spectral Procedures
440800 -- Miscellaneous Instrumentation-- (1990-)
47 OTHER INSTRUMENTATION
CONSTRUCTION
ELECTRON SPIN RESONANCE
EPR SPECTROMETERS
FREQUENCY RANGE
FREQUENCY SELECTION
G MATRIX
GHZ RANGE
GHZ RANGE 01-100
HETEROCYCLIC COMPOUNDS
MAGNETIC RESONANCE
MATRICES
MEASURING INSTRUMENTS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
POLYCYCLIC SULFUR HETEROCYCLES
RESONANCE
SPECIFICATIONS
SPECTROMETERS