Fundamental defect centers in glass:Si29hyperfine structure of the nonbridging oxygen hole center and the peroxy radical ina-SiO2

${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ hyperfine structure determinations for two fundamental oxygen-associated paramagnetic defect centers in high-purity amorphous silica complete the characterization of the nonbridging oxygen hole center and the peroxy radical by demonstrating in each case that the oxygen(s) trapping the unpaired spin are bonded to only one silicon in the glass network. It is shown that these findings place important constraints on the supposed precursors of the peroxy radical in $a$-Si${\mathrm{O}}_2$.