The ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ hyperfine structure of the anomalous muonium center in silicon has been resolved in muonspin-rotation spectra. The spectra of the weak ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ satellite lines show that there are two equivalent Si neighbors on the <111> symmetry axis with large positive $p$-like spin densities. These results, which are confirmed by level-crossing-resonance spectroscopy, establish that anomalous muonium in the group-IV semiconductors is an interstitial muonium located at the bond center.

• Received 21 August 1987

DOI:https://doi.org/10.1103/PhysRevLett.60.224