Electron spin resonance of a di-nitrogen centre in Cape yellow type Ia diamonds

Abstract
A di-nitrogen centre has been observed in gem quality Cape yellow diamonds while illuminated with ultraviolet light. Analysis of the spectrum shows that the paramagnetic electron is localised on two neighbouring nitrogens along (111) directions, which suggests that it is most likely a derivative of the non-paramagnetic A centre. Observation of this paramagnetic centre in many diamonds suggests an interplay between it, the A centre, the P2 (or optical N3) and possibly the P1 centre.