Electron Spin Resonance Spectra associated with Nitrogen in Diamonds

Abstract

MANY diamonds show an electron spin resonance spectrum which has been attributed to the presence of single nitrogen atoms substituted for carbon at a diamond lattice site. Smith et al.¹ found four types of nitrogen donors, equally abundant and differing only in their hyperfine axes, these being the four C–N bond directions. They measured the hyperfine coupling constants for ¹⁴N(I=1), and for ¹³C(I = ½) in the nearest neighbour positions (denoted centre I). Loubser and du Preez² found additional lines in the spectrum, which they attributed to interaction of the unpaired electron with carbon-13 at other lattice sites (centres II, III and IV). The hyperfine coupling constants are recorded in Table 1, together with the orbital populations. These populations were obtained using values of ∣ψ_2s(0)∣² and 〈r⁻³〉_2p calculated from self-consistent-field atomic wave functions derived by Mayers and by Roothaan and Clementi (see ref. 3). (We have omitted any correction for the δ+ charge on nitrogen and the δ− charge on carbon: this would increase the spin density on carbon at the expense of the nitrogen.)