Abstract
in glass and crystalline states have been subjected to γ irradiation at room temperature and subsequently studied by continuous-wave electron paramagnetic resonance and electron-spin-echo envelope modulation (ESEEM) spectroscopy at liquid-helium temperature. The ESEEM study of revealed the existence of weak magnetic couplings between the irradiation-induced paramagnetic centers and nearby nuclei. The assignment of the observed couplings was achieved by the use of the two-dimensional hyperfine sublevel correlation spectroscopy. A detailed theoretical analysis of the ESEEM spectra and a system in both time and frequency domain is also presented. Computer simulation of the spectra, Hartree-Fock self-consistent field, and modified neglect of differential overlap calculations revealed that the unpaired electron in the glass is associated with a dangling bond of oxygen attached to a boron of a boroxol ring. The paramagnetic centers of the crystal are associated with oxygen dangling bonds in boron trigonal units. Pertinent structural models for the glass are examined at a microscopic level.
- Received 3 February 1998
DOI:https://doi.org/10.1103/PhysRevB.58.11420
©1998 American Physical Society