ELECTRON-PARAMAGNETIC-RESONANCE MEASUREMENTS ON THE DI-[001]-SPLIT INTERSTITIAL CENTER (R1) IN DIAMOND

Electron-paramagnetic-resonance (EPR) studies in electron-irradiated d iamond enriched with 5% C-13 have resulted in identification of the di -[001]-split interstitial center. II is the isotopic enrichment and th e consequent observation of C-13 hyperfine satellites that have permit ted the structure to be determined more than 30 years after the discov ery of the center. Analysis of the C-13 hyperfine couplings by a simpl e molecular orbital calculation shows that the center may be viewed as a biradical consisting of two unpaired electrons, each primarily loca lized in a nonbonding 2p orbital, on different carbon atoms. The excha nge interaction between these electrons results in a spin-tripler grou nd state which is well separated from the singlet excited state. The z ero-field splitting observed in EPR is dipolar in origin and, taken to gether with the distribution of the unpaired electron population, indi cates that the carbon atoms with the nonbonding 2p orbitals are separa ted by about 2.2 Angstrom. The center has sigma(h) symmetry. Formation of the di-[001]-split interstitial by room temperature irradiation co nfirms that the interstitial is mobile at this temperature. Identifica tion of this center suggests a [001]-split interstitial configuration for the carbon self-interstitial, a fundamental defect which has so fa r eluded direct detection.