Electronic structure of B2O3 glass studied by one- and two-dimensional electron-spin-echo envelope modulation spectroscopy

B2O3 in glass and crystalline states have been subjected to gamma 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 B2O3 revealed the existence of wreak magnetic couplings between the irradiation-induced paramagnetic centers and nearby B-10, B-11 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 a and a S = 1/2 I =3/2 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 B2O3 glass is associated with a dangling bond of oxygen attached to a boron of a boroxol ring. The paramagnetic centers of the B2O3 crystal are associated with oxygen dangling bonds in boron trigonal units. Pertinent structural models for the glass B2O3 are examined at a microscopic level. [S0163-1829(98)01341-1].