Identification of the di-nitrogen <001> split interstitial H1a in diamond

The structure of the defect responsible for the H1a absorption feature in diamond has been much debated. In this work, the results of uniaxial stress-splitting studies are compared to piezospectroscopic stress-splitting parameters calculated for the <001> di-nitrogen split interstitial (N_2I) defect. The stress-splitting data shows that the H1a absorption band arises from an A–E transition at a center with D_2d symmetry. Furthermore, the experimentally and theoretically determined stress-splitting parameters are in excellent agreement, supporting the assignment of the H1a band to the N_2I defect.