Electron paramagnetic resonance of the ${\mathrm{N}}_2{\mathrm{V}}^{-}$ defect in ${}^{15}\mathrm{N}$-doped synthetic diamond

Nitrogen is the dominant impurity in the majority of natural and synthetic diamonds, and the family of nitrogen vacancy-type (${\mathrm{N}}_{\mathrm{n}}\mathrm{V}$) defects are crucial in our understanding of defect dynamics in these diamonds. A significant gap is the lack of positive identification of ${{\mathrm{N}}_2\mathrm{V}}^{-}$, the dominant charge state of ${\mathrm{N}}_2\mathrm{V}$, in diamond that contains a significant concentration of electron donors. In this paper we employ isotopically-enriched diamond to identify the EPR spectrum associated with ${}^{15}{{\mathrm{N}}_2\mathrm{V}}^{-}$ and use the derived spin Hamiltonian parameters to identify ${}^{14}{{\mathrm{N}}_2\mathrm{V}}^{-}$ in a natural isotopic abundance sample. The electronic wavefunction of the ${\mathrm{N}}_2{\mathrm{V}}^{-}$ ground state and previous lack of identification is discussed. The ${{\mathrm{N}}_2\mathrm{V}}^{-}$ EPR spectrum intensity is shown to correlate with H2 optical absorption over an order of magnitude in concentration.