Electron nuclear double resonance study of a nitrogen centre in diamond

Endor measurements on a type 1b diamond with paramagnetic nitrogen centres were made at 4$\cdot$2, 77 and 300 $^\circ$K by means of a 35 000 Mc/s spectrometer. The axially symmetric nitrogen hyperfine coupling and quadrupole coupling parameters at 4$\cdot$2 $^\circ$K are $$A_{\mathrm{iso}.} = 92\cdot228 \pm 0\cdot001,\, A_{\mathrm{aniso}.} = 10\cdot903 \pm 0\cdot002,\, P = -3\cdot974 \pm 0\cdot001 Mc/s.$$ A small change of hyperfine coupling with temperature was observed.