Electron paramagnetic resonance of the $\mathrm{N_{2}V^{-}}$ defect in $\mathrm{^{15}N}$-doped synthetic diamond

Nitrogen is the dominant impurity in the majority of natural and synthetic diamonds, and the family of nitrogen vacancy-type ($\mathrm{N_{n}V}$) defects are crucial in our understanding of defect dynamics in these diamonds. A significant gap is the lack of positive identification of $\mathrm{N_{2}V}^{-}$, the dominant charge state of $\mathrm{N_{2}V}$, 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 $^{15}\mathrm{N_{2}V}^{-}$ and use the derived spin Hamiltonian parameters to identify $^{14}\mathrm{N_{2}V}^{-}$ in a natural isotopic abundance sample. The electronic wavefunction of the $\mathrm{N_{2}V^{-}}$ ground state and previous lack of identification is discussed. The $\mathrm{N_{2}V}^{-}$ EPR spectrum intensity is shown to correlate with H2 optical absorption over an order of magnitude in concentration.