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Electron-spin resonance of bound substitutional nitrogen donors in diamond is observed and discussed. The g factor is isotropic at 2. 00240. 0005. For a given donor, one of the C-N bond directions is a hyperfine axis with constants A=40. 8 oersteds, B=29. 2 oersteds. There are thus four types of donors, equally abundant. A model for the donor wave function is proposed which puts the donor electron principally into an antibonding orbital located on a nitrogen atom and on one of its nearest-neighbor carbon atoms. A C-N bond distortion results which can be regarded as a manifestation of the Jahn-Teller effect. A careful search reveals the presence of an additional weak spectrum due to donors on N^14-C^13 pairs. (The isotope C^13 which has a nuclear spin of has a natural abundance of 1. 1%. ) The hyperfine constants measured for a C^13 atom of an N-C pair are A^'=60. 8 oersteds, B^'=25. 3 oersteds. The s and p contributions to all 4 measured hyperfine constants are separated to give the values O₍= (83) {| (0) |^2}₍=2. 41 atomicunits, P₍=〈{z^{2-12 (x^2+y^2) }{r^5}〉}₍=0. 28 atomicunit, O₂= (83) {| (0) |^2}₂=0. 78 atomicunit, P₂=〈{z^{2-12 (x^2+y^2) }{r^5}〉}₂=0. 25 atomicunit. These are compared with theoretical values obtained by assuming a simple antibonding wave function composed of nitrogen and carbon tetrahedral orbitals. An increase of several percent in the N-C separation along the hyperfine axis is strongly implied by the comparison.
Smith et al. (Tue,) studied this question.