Electron paramagnetic resonance measurements were made of synthetic specimens which had been grown in an Fe-Ni-C solvent/catalyst system at 1750K, under pressure, using the temperature-gradient method. Such diamonds had high H contents. Electron paramagnetic resonance spectra were found in 3 well-separated regions. The first of these spectra consisted of a family of lines around the electron paramagnetic resonance spectrum of the P1 center (isolated Ns). The second spectrum consisted of a family of weak lines at about one-half of the P1 magnetic field. The third consisted of a family of weak lines at about twice the P1 magnetic field. The first spectrum was attributed to the defect centers: NOC1, NOC2 and NOC3. Each of the centers corresponded to a pair of Ns atoms with different separations. The second spectrum, NOC4, was also attributed to separated pairs of Ns atoms, but was a superposition of spectra from all pairs with separations greater than about 0.7nm. The third spectrum was attributed to isolated P1 centers which were resonated by a 2 microwave photon transition.

EPR Spectra of Separated Pairs of Substitutional Nitrogen Atoms in Diamond with a High Concentration of Nitrogen. V.A.Nadolinny, A.P.Yelisseyev, J.M.Baker, D.J.Twitchen, M.E.Newton, A.Hofstaetter, B.Feigelson: Physical Review B, 1999, 60[8], 5392-403